ChatGPT answers, unedited

Klaviyo is probably the strongest fit for an ecommerce-focused agency. It supports multiple client accounts under one login, centralized portfolio management, and both email + SMS per client. Klaviyo Help Center Klaviyo Help Center Klaviyo Help Center

If you want white-labeling + CRM + broader agency operations, HighLevel is worth comparing; if you want deep ecommerce segmentation, flows, and revenue attribution, Klaviyo is more purpose-built. tooldecisionengine.com

For an agency managing multiple ecommerce clients, I’d look at Klaviyo first if the priority is ecommerce email/SMS performance, while HighLevel is better if the priority is one agency dashboard with client sub-accounts and white-labeling. Tool Decision Engine GoHighLevel

• Klaviyo: strongest for Shopify/ecommerce segmentation, flows, purchase data, and revenue attribution. Check Charm - the best things and places
• HighLevel: strongest for centralized agency management, multiple client accounts, email + SMS, CRM, and white-labeling. GoHighLevel
• Practical agency setup: Klaviyo for ecommerce execution + an agency-management layer if you need centralized client operations.

If you tell me how many clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, I can narrow it down.

If you’re an agency managing multiple ecommerce clients and need both email + SMS from one interface, I’d narrow it to HighLevel vs. Klaviyo.

My pick: Klaviyo for ecommerce agencies

Klaviyo is probably the better fit if your clients are primarily Shopify/DTC brands. It’s built around ecommerce data, segmentation, revenue attribution, abandoned-cart flows, post-purchase automation, and coordinated email/SMS campaigns.

Klaviyo now supports multiple accounts under one login, plus portfolios that give agencies a high-level view across multiple accounts. Klaviyo Help Center Klaviyo Help Center

The downside is that it's still fundamentally one account per ecommerce business, rather than a true agency operating system.

Pick HighLevel if agency management is the priority

HighLevel is stronger if you want one agency dashboard containing many client sub-accounts, with email, SMS, CRM, automation, conversations, reporting, and potentially white-labeling.

HighLevel specifically supports separate client sub-accounts, centralized agency management, cloning workflows, and a unified inbox. GoHighLevel HighLevel Support Portal Its Agency Unlimited plan currently supports unlimited sub-accounts, while Pro adds SaaS/white-label capabilities. GoHighLevel

Quick decision

So if you mean “I run an ecommerce marketing agency with 10–50 Shopify clients and my team needs to jump between their email/SMS accounts,” I'd start with Klaviyo.

If you mean “I want my agency to operate everything for clients from one master dashboard and potentially sell the software itself,” I'd choose HighLevel.

One interesting wrinkle: Klaviyo also has shared billing for account families, although self-serve shared billing is currently limited to 20 accounts, so that's more useful for related brands than a large agency client roster. Klaviyo Help Center

If you tell me roughly how many clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, I can give you a much more specific recommendation—including pricing and the best agency setup.

For an agency managing multiple ecommerce clients and needing both email + SMS from one interface, I’d put HighLevel and Klaviyo at the top—but they solve slightly different problems.

My pick: HighLevel

gohighlevel.com is the better agency operating system.

• Multiple client accounts: clients live in separate sub-accounts, while your team manages them from an agency dashboard. HighLevel Support Portal HighLevel Support Portal
• Email + SMS together: both channels are built into the platform, including bulk SMS and email campaigns. HighLevel Support Portal
• Agency/white-label capabilities: you can brand the platform and even resell it as SaaS. GoHighLevel HighLevel Support Portal
• Scaling: the $297/month Agency Unlimited plan currently includes unlimited sub-accounts; the $497 Pro plan adds SaaS functionality. GoHighLevel
• Centralized management: HighLevel has been adding agency-level controls and bulk management specifically for multi-client operations. HighLevel Support Portal HighLevel Support Portal

But if you're a pure ecommerce retention agency: Klaviyo

klaviyo.com is probably the stronger ecommerce marketing platform.

It has excellent ecommerce segmentation, flows, behavioral triggers, and revenue attribution. It also supports email and SMS, and you can access multiple client accounts from one login. Klaviyo Help Center

The tradeoff is that Klaviyo is fundamentally organized around one account per ecommerce store, whereas HighLevel is designed around an agency → sub-account → client hierarchy.

Quick decision

Bottom line: If you're building an agency where the interface itself needs to be organized around multiple clients, I'd choose HighLevel. If your agency's core product is high-end Shopify lifecycle/email/SMS marketing, I'd choose Klaviyo.

If you tell me roughly how many ecommerce clients you manage and whether they're mostly Shopify, I can narrow it down further—including pricing, white-labeling, client access, SMS costs, and automation capabilities.

If you’re an agency managing multiple ecommerce clients, I’d narrow it to two serious choices: HighLevel and Klaviyo.

My pick: HighLevel for the agency, Klaviyo for the ecommerce specialist

HighLevel is probably the best fit if your priority is literally “I want one agency interface where my team can manage email + SMS for 10, 50, or 100 clients.” It has agency-level sub-accounts, centralized administration, bulk management, and email/SMS functionality. Recent 2026 updates have also added more agency-level filtering and bulk account management. HighLevel Support Portal HighLevel Support Portal HighLevel Support Portal

gohighlevel.com

Klaviyo is the better choice if your agency's core service is ecommerce retention—especially Shopify brands. Its segmentation, customer/event data, revenue attribution, and email/SMS automation are considerably more ecommerce-centric. Klaviyo also supports multiple accounts under one login, so your team can switch between client accounts without separate credentials. Klaviyo Help Center

klaviyo.com

The important distinction

If you're selling:

“We manage your entire marketing/CRM system.”

→ HighLevel

If you're selling:

“We grow your Shopify store's revenue through email + SMS.”

→ Klaviyo

For a pure ecommerce agency, I'd lean Klaviyo despite the less agency-native interface. For a broader marketing agency where having every client under one operational umbrella is the priority, I'd choose HighLevel.

There are also Omnisend and Brevo worth considering if price/ease of deployment matters more than advanced agency infrastructure; Omnisend in particular is positioned around ecommerce email + SMS. mailercloud.com

If you tell me roughly how many ecommerce clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can give you a much more specific recommendation—including which is cheapest at your scale and which gives the agency the best margins.

For an agency managing multiple ecommerce clients and needing email + SMS from one interface, the best fit is usually a platform with:

• Multi-account/client management
• Separate client workspaces
• Ecommerce integrations (Shopify, BigCommerce, WooCommerce, etc.)
• Shared templates/automation workflows
• Reporting you can present to clients
• Permission controls
• White-label or agency-friendly features

The strongest options:

My top pick for most ecommerce agencies: Klaviyo

klaviyo.com is usually the best agency choice because it was built around ecommerce lifecycle marketing: email, SMS, segmentation, flows, customer profiles, and revenue attribution in one system. Blossom Fairview

Why agencies like it:

• Each client can have their own Klaviyo account/workspace.
• Easy to build repeatable services: - Welcome flows
• Abandoned cart
• Browse abandonment
• Post-purchase
• Winback
• Product launches
• VIP campaigns
• Strong Shopify data integration.
• Clients can see revenue attribution instead of just opens/clicks. Fairview

The downside: you generally manage each client account separately rather than having one giant “agency dashboard.”

If your agency is SMS-first: Attentive

attentive.com is stronger when SMS is the main revenue driver. It combines SMS and email capabilities and focuses heavily on mobile engagement, conversational messaging, and enterprise support. Attentive Attentive

Good fit for:

• Fashion
• Beauty
• Supplements
• High-volume Shopify Plus brands
• Clients spending heavily on SMS

Less ideal if you manage many smaller brands because it tends to be more enterprise-oriented. Fairview

Good budget-friendly agency option: Omnisend

omnisend.com is worth considering if your clients are smaller ecommerce stores and you want faster setup with email + SMS automation without enterprise pricing.

What I would choose by agency size

1–10 ecommerce clients

• Start with Klaviyo
• Create repeatable flows and reporting templates

10–50 clients

• Still likely Klaviyo
• Build internal SOPs, templates, and onboarding checklists

50+ clients / enterprise portfolio

• Consider: - Klaviyo for most clients
• Attentive for high-volume SMS clients
• Possibly an agency CRM layer on top

One thing to watch out for

Avoid platforms designed mainly for sending newsletters. Ecommerce clients usually pay agencies for revenue-generating automations, not just campaigns. The platform should make it easy to prove:

• recovered carts
• repeat purchases
• customer lifetime value
• SMS revenue
• flow performance

If you tell me:

1. how many ecommerce clients you manage,
2. whether they are mostly Shopify, WooCommerce, or something else, and
3. whether you want one login/dashboard for all clients vs separate client accounts,

I can narrow this down to the best agency stack.

For an agency managing email + SMS for multiple ecommerce clients, I’d put Klaviyo at the top of the list.

My ranking

1. Klaviyo — best overall

• Email + SMS in the same platform, customer profiles, segments, flows, analytics, and attribution.
• You can manage multiple client accounts from one login and switch between them without separate credentials. Klaviyo Help Center
• Particularly strong if your clients are primarily Shopify/DTC.
• Best choice if your agency wants to standardize its processes across dozens of accounts.
• Attentive — best for larger clients

• Stronger fit when clients are enterprise or heavily SMS-focused.
• Has an agency partner program specifically designed to support agencies managing customer programs across SMS, email, RCS and push. Attentive
• More appropriate when clients have large SMS lists and substantial messaging budgets.
• Omnisend — best lower-cost alternative

• Email + SMS with ecommerce-oriented automation.
• Worth considering if your clients are smaller and you don't need the depth of Klaviyo's segmentation/data infrastructure.

What I'd choose for an agency

If your agency looks something like:

10–50 Shopify stores → each client gets email + SMS → your team manages campaigns, flows, reporting and strategy

I'd standardize on Klaviyo.

The important distinction is that you don't want merely an email platform plus an SMS platform. You want one customer database and orchestration layer, so an abandoned-cart/customer journey can decide whether to send email, SMS, or both based on the same customer behavior. Klaviyo's unified email/SMS architecture is particularly good for this. US Tech Automations Subjectlime | Klaviyo Agency

One caveat: if by "single interface" you mean one agency dashboard where you can see all clients' campaigns, revenue, tasks, approvals, billing, and performance without actually switching into individual Klaviyo accounts, that's a somewhat different requirement. In that case, I would evaluate an agency/client-management layer on top of Klaviyo, rather than just choosing an ESP.

If you tell me roughly how many ecommerce clients you manage (5, 20, 100+) and whether they're mostly Shopify, I can give you a much more specific recommendation and compare Klaviyo vs Attentive vs Omnisend vs an agency-specific white-label platform.

For an agency managing multiple ecommerce clients, I’d shortlist Omnisend, Klaviyo, and Attentive. Of those, Omnisend is probably the best fit if your #1 requirement is managing many client stores from a single interface.

My ranking

1. Omnisend — best overall for your use case

Omnisend explicitly supports multiple stores, letting you switch between stores from one login. It also lets agencies use separate client accounts while giving the agency team access across them. www.omnisend.comconnect.klaviyo.comwww.attentive.comsupport.omnisend.com

The particularly interesting part for an agency is its Partner Portal: you can create templated accounts and build automations, campaigns, and signup forms once, then copy them into multiple client stores. support.omnisend.com

It supports email + SMS + push, with ecommerce data such as products, orders, and customers feeding into campaigns and automations. support.omnisend.com

2. Klaviyo — best if your clients are primarily Shopify/DTC brands

Klaviyo is probably the safer choice if you're selling a premium lifecycle marketing service rather than simply wanting the easiest multi-store dashboard. It has a huge agency ecosystem, sophisticated segmentation/flows, and unified email/SMS capabilities. connect.klaviyo.com

I'd pick Klaviyo over Omnisend if your clients are generally larger Shopify brands and you need deeper customization, analytics, integrations, and advanced lifecycle marketing.

3. Attentive — best if SMS is the centerpiece

Attentive is particularly strong when SMS/conversational messaging is a major part of the service. Its platform combines SMS and email and has an agency partner program specifically designed around agencies serving shared customers. www.attentive.com

What I'd choose

If you're building an agency where the workflow is:

Client A → Client B → Client C → Client D → manage campaigns/flows/SMS from one agency login

I'd start with Omnisend.

If the workflow is:

High-value Shopify clients → sophisticated segmentation → advanced flows → serious revenue attribution → premium agency retainers

I'd choose Klaviyo.

If it's:

SMS-heavy DTC marketing → conversational SMS → email + SMS coordination

I'd choose Attentive.

One important distinction: "single interface" doesn't necessarily mean one shared client database. Omnisend's model keeps each store's contacts, automations, statistics, and reports separate while allowing you to switch/manage them centrally. That's actually preferable for an agency because it maintains client data isolation. www.omnisend.comconnect.klaviyo.comwww.attentive.comsupport.omnisend.com

If you tell me how many clients you expect (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can narrow this down to the best platform and compare agency pricing, client permissions, white-labeling, billing, and multi-account management.

For an agency managing multiple ecommerce clients from one interface, the best tool depends on whether you prioritize true multi-client management, ecommerce revenue features, or white-label resale. The strongest options are:

Excelohunt BestSends### My shortlist by agency model

1. Ecommerce retention agency (Shopify brands, DTC, lifecycle marketing)
→ Klaviyo is usually the best choice. It keeps email and SMS tied to the same customer data, which makes flows like abandoned cart → SMS reminder → post-purchase → winback much easier to manage. Excelohunt

2. Agency that wants one login, client workspaces, and to resell the software
→ GoHighLevel is the closest fit. It is designed around agencies managing many client accounts, with sub-accounts and white-label options. Sequenzy

3. Agency serving many smaller ecommerce clients on retainers
→ Brevo can make sense because pricing and multi-channel messaging are often simpler to scale across many smaller lists. Hack'celeration

What I would avoid

• Using separate tools like one email platform + one SMS platform per client unless there is a strong reason. It creates reporting, segmentation, and compliance headaches.
• Giving every client a completely different stack. Agencies usually become more profitable when they standardize around 1–2 platforms. BestSends

Practical recommendation

For most ecommerce agencies:

• 1–20 Shopify/DTC clients: Klaviyo as the core platform.
• 20+ clients where you sell “marketing as a service”: GoHighLevel.
• Mixed clients (ecommerce + local businesses + lead gen): GoHighLevel or ActiveCampaign.
• High-volume DTC brands: Klaviyo, sometimes paired with specialized SMS tools. Excelohunt BMO Media

If you mean “one dashboard where my team can log in and manage 50+ ecommerce clients without switching accounts”, the answer shifts more toward GoHighLevel or an agency-specific setup rather than a pure ecommerce tool.

For an agency managing multiple ecommerce clients and needing both email + SMS from one interface, the best choice depends on whether you want an ecommerce retention platform or an agency operating system.

My shortlist:

Hack'celeration BestSends## My recommendation by agency type

If you mainly serve Shopify/DTC brands

Choose Klaviyo.

It is usually the strongest stack for:

• abandoned cart flows
• post-purchase sequences
• VIP/customer segmentation
• product recommendations
• revenue attribution
• email + SMS coordination

Many ecommerce agencies standardize on Klaviyo because the client results are easier to prove. Excelohunt BestSends

If you want one dashboard for 20–500 clients

Choose GoHighLevel.

It is better when your business model is:

• “we sell marketing as a service”
• each client gets their own workspace
• account managers need access
• you want white-label reporting
• you want to bundle CRM + SMS + email + funnels

Tool Decision Engine### If you want the closest thing to an agency command center

Look at:

• GoHighLevel for operations
• Klaviyo for ecommerce revenue work

Some mature agencies actually use both:

• GoHighLevel → client management, CRM, reporting, sales pipeline
• Klaviyo → ecommerce retention campaigns

What I would avoid

I would avoid building an agency around separate tools like:

• Mailchimp + Twilio + spreadsheets
• one-off SMS tools per client
• manually logging into every brand account

The operational overhead becomes painful once you have more than a handful of clients.

Quick decision rule

• 5–50 Shopify brands: Klaviyo
• 50+ mixed business clients: GoHighLevel
• Small clients where margin matters: Brevo
• Complex automation consulting: ActiveCampaign

If you tell me roughly how many clients you manage, whether they are Shopify/WooCommerce, and whether you need white-label client logins, I can narrow it to one stack.

If you're an agency managing email + SMS for multiple ecommerce clients, I’d shortlist Omnisend and Klaviyo, with Omnisend probably the better fit if the multi-client workflow is your priority.

My ranking

1. omnisend.com — best agency/multi-client fit

• Built specifically around ecommerce.
• Lets you manage multiple stores from one login and switch between them.
• Email, SMS, and push are managed in the same platform.
• Its Partner Portal supports agency workflows, including reusable templated accounts where you can build automations/campaigns/forms once and copy them to client stores. Omnisend Omnisend Help Center
• You can keep clients separated with their own stores, billing, data, permissions, and reporting. Omnisend Help Center
• klaviyo.com — best for sophisticated clients

• Excellent if your clients are serious DTC brands and need sophisticated segmentation, flows, attribution, and CRM functionality.
• Supports multiple Klaviyo accounts under one login, so your team can switch between clients without logging in/out. Klaviyo Help Center
• Email + SMS live together, which is particularly useful for cross-channel flows.
• I'd choose this over Omnisend if advanced marketing sophistication matters more than agency operational simplicity.
• attentive.com — best if SMS is the centerpiece

• Strong option for larger ecommerce clients where SMS/RCS is particularly important.
• Has an agency partner program spanning SMS, email, RCS and push. Attentive
• But I'd generally put it behind Klaviyo/Omnisend for an agency wanting a unified ecommerce email + SMS operating system.

What I'd pick for an agency

For the exact use case you described, I'd start with Omnisend. Its agency-specific Partner Portal and multi-store architecture are unusually well aligned with "one agency → many ecommerce clients." Omnisend Help Center Omnisend Help Center

If you tell me roughly how many clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can also compare Omnisend vs Klaviyo specifically on agency pricing, client separation, permissions, white-labeling, reporting, and bulk campaign/flow deployment.

If you're an agency managing email + SMS for multiple ecommerce clients, I'd narrow it to Klaviyo vs. Omnisend, with the right choice depending on whether you prioritize ecommerce depth or agency-style multi-client management.

My pick: Klaviyo

klaviyo.com is probably the best fit if your clients are primarily Shopify/DTC brands.

• Email + SMS in the same platform — shared profiles, segmentation, flows, consent, and reporting.
• Multiple client accounts under one login — you can switch between separate client accounts without logging out. Klaviyo Help Center
• Excellent ecommerce data and automation: abandoned cart, post-purchase, winback, browse abandonment, etc.
• Stronger choice if your agency is selling retention/revenue growth, rather than simply sending campaigns.
• Large ecosystem of ecommerce integrations.

The downside is that it isn't really an agency "command center." Each client still has their own account, billing, data, etc.

Strong alternative: Omnisend

omnisend.com is particularly interesting if managing lots of smaller ecommerce clients is the priority.

Omnisend explicitly supports multi-store management, including switching between stores, copying templates/workflows between stores, and managing email + SMS + push from one account. It currently supports up to 500 stores under one account. Omnisend Omnisend Help Center

Its documentation also specifically recommends the separate-account setup for partners/agencies managing stores for different clients, while allowing the agency user to access multiple accounts. Omnisend Help Center

How I'd choose

attentive.com is worth considering for large, SMS-heavy brands, but I'd generally favor Klaviyo for an ecommerce agency because email and SMS live more naturally together in the ecommerce workflow. Attentive

One important distinction: if by "single interface" you mean one dashboard where your agency can see all clients, switch accounts, manage campaigns, report results, and potentially white-label the experience to clients, rather than simply "one login," then I'd evaluate HighLevel differently from Klaviyo/Omnisend.

If you tell me roughly how many ecommerce clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can give you a much more specific recommendation, including pricing and agency workflow.

If you mean an agency managing email + SMS campaigns for multiple ecommerce brands from one login, I’d narrow it to three choices:

My recommendation

For a serious ecommerce agency: Klaviyo.

It has the strongest ecommerce-specific capabilities—Shopify integrations, segmentation, revenue attribution, flows, product/customer data, and sophisticated email/SMS automation. Its partner ecosystem is also particularly strong for agencies. Ecommerce Times Check Charm - the best things and places

For an agency that prioritizes one centralized agency interface: HighLevel.

HighLevel was designed around the agency model: client sub-accounts, centralized management, email + SMS, CRM, automation, reporting, white-labeling, and rebilling. GoHighLevel Tool Decision Engine

Omnisend is the interesting middle ground. It explicitly supports multiple stores, lets you switch between them, reuse templates/workflows, and manage email/SMS/push from one account. Omnisend

The key distinction

If your agency is essentially:

"We are an ecommerce retention agency and manage Klaviyo/SMS for 20 Shopify brands."

→ Klaviyo

If it's:

"We want one agency platform where every client has an account, we manage email/SMS, automate things, and potentially resell the software under our brand."

→ HighLevel

If it's:

"We manage lots of smaller Shopify stores and want email + SMS without Klaviyo's complexity/cost."

→ Omnisend

There are also newer agency-first white-label platforms worth investigating if your biggest concern is one dashboard + isolated client accounts + your own branding + centralized billing, rather than having the deepest ecommerce marketing engine. IGSendMail NotifyBulk

If you tell me roughly how many ecommerce clients you manage (e.g. 5, 25, 100+) and whether they're mostly Shopify, I can tell you which one I'd pick and why—including the agency pricing/margins and client-account structure.

If you mean an agency managing multiple ecommerce brands, with both email + SMS and wanting as much as possible under one agency-level interface, I’d narrow it to HighLevel vs. Klaviyo.

My pick: HighLevel for the agency

gohighlevel.com is probably the better fit if the agency itself is the center of operations.

• Multiple client accounts: HighLevel is built around agency → sub-account architecture, so each ecommerce client can have its own isolated account. HighLevel Support Portal HighLevel Support Portal
• Email + SMS: Both are native channels, including bulk SMS, email campaigns, workflows, and a unified conversation inbox. HighLevel Support Portal GoHighLevel
• Agency controls: You can manage users, permissions, email services, and multiple sub-accounts from the agency view. HighLevel Support Portal HighLevel Support Portal
• Reusable systems: HighLevel lets agencies deploy snapshots/workflows across client accounts, which is particularly useful if you have standardized onboarding and campaign frameworks. HighLevel Support Portal
• White-label/SaaS: Higher tiers support unlimited sub-accounts, white-labeling, and rebilling, which is useful if you're selling the platform as part of your service. GoHighLevel

But Klaviyo wins for pure ecommerce marketing

klaviyo.com is the one I'd choose if your agency's primary job is ecommerce retention/revenue rather than general client CRM.

Klaviyo is much more ecommerce-native for things like product/customer data, segmentation, abandoned cart, post-purchase, predictive analytics, revenue attribution, and sophisticated email/SMS journeys. It also now supports multi-account management and portfolios, allowing agencies/organizations to access multiple accounts with one login and get a high-level view across them. Klaviyo Help Center Klaviyo Help Center

The decision

So if your exact requirement is: “I want one agency login/interface where my team can manage email + SMS campaigns for lots of different ecommerce clients” → HighLevel is the better agency operating system.

If it's: “We're an ecommerce retention agency and need the best possible email/SMS engine for each Shopify brand” → Klaviyo is probably better, even though you'll be managing separate client accounts.

One important distinction: neither really turns 50 independent ecommerce stores into one shared marketing database. The client accounts remain separated; the advantage is centralized agency access/management.

If you tell me roughly how many ecommerce clients you manage (e.g. 5, 20, 100+) and whether they're mostly Shopify, I can give you a much more specific recommendation—including HighLevel vs Klaviyo vs Omnisend vs Brevo and which is likely cheapest at your scale.

For an agency managing multiple ecommerce clients and needing both email + SMS from one interface, the best choice depends on whether you prioritize ecommerce revenue performance or agency operations.

Best overall picks

My recommendation by agency type

If you are an ecommerce retention agency → choose Klaviyo

This is usually the strongest fit if your clients are Shopify/DTC brands. You can build repeatable playbooks:

• Welcome series
• Abandoned cart flows
• Browse abandonment
• Post-purchase upsells
• Customer win-back
• SMS campaigns
• Revenue reporting

The downside: it is more brand-account focused than agency-dashboard focused, so managing dozens of clients can become operationally heavy. Check Charm - the best things and places

If you want one dashboard for many clients → choose HighLevel

HighLevel is designed around the agency model:

• Separate client sub-accounts
• Shared agency login
• Email + SMS
• Automations
• CRM
• White-label capabilities

It is a better operational fit if your team manages many businesses and you sell a broader marketing service. Tool Decision Engine

If you want a true multi-client messaging workspace → look at agency-first tools

Some newer platforms are specifically positioning around agencies managing multiple client workspaces from one login, including separate contacts, campaigns, reporting, and billing structures. Examples include Messaro and NotifyBulk. Messaro NotifyBulk

What I would avoid for this use case

• Mailchimp: fine for individual brands, but awkward when you have many ecommerce clients.
• Twilio alone: powerful infrastructure, but you will have to build the agency layer yourself.
• Enterprise SMS-only tools: often excellent for one large retailer but not designed for managing 20–100 smaller clients. Havari

Short answer

• 5–20 ecommerce clients, focused on revenue growth: Klaviyo
• 20+ clients, full-service agency model: HighLevel
• Need white-label / client workspaces: HighLevel or an agency-first platform
• Need the deepest ecommerce performance analytics: Klaviyo

If you tell me roughly how many clients you manage (5, 20, 100+) and whether they are mostly Shopify stores, I can narrow it down to the best operational fit.

For an agency managing multiple ecommerce clients and wanting email + SMS from a centralized interface, I’d shortlist these:

My pick: Omnisend

For your exact use case, Omnisend is probably the best fit if your clients are primarily Shopify/BigCommerce/WooCommerce ecommerce brands.

Omnisend lets you manage multiple stores, switch between them without logging in/out, reuse templates and workflows, and manage email, SMS and push within the same platform. It explicitly supports an agency/partner model where separate client accounts can retain their own ownership and billing while your agency users access them. Omnisend Omnisend Help Center

It also has a particularly useful Partner Portal + templated accounts feature: your agency can build automations, campaigns, signup forms, etc. once and copy them into client stores. Omnisend Help Center

omnisend.com

When I'd choose Klaviyo instead

Choose Klaviyo if your agency's competitive advantage is sophisticated ecommerce lifecycle marketing—complex segmentation, flows, personalization and revenue attribution.

Klaviyo now supports portfolios specifically for agencies, giving you a high-level view across multiple client accounts, and you can switch between multiple accounts with one login. Klaviyo Help Center Klaviyo Help Center

klaviyo.com

The downside is that it's more account-centric than agency-centric. Each ecommerce store generally has its own Klaviyo account, so the centralized experience isn't quite as purpose-built for an agency as an agency CRM platform. Klaviyo Help Center

When I'd choose HighLevel

If you're not just doing ecommerce retention, but want your agency to provide CRM + email + SMS + automations + pipelines + lead management under one client-management system, HighLevel becomes very compelling.

It supports email and SMS directly, including bulk and scheduled SMS, within its client accounts. HighLevel Support Portal

gohighlevel.com

My ranking for an ecommerce email/SMS agency:

1. Omnisend — best overall agency + ecommerce combination
2. Klaviyo — best marketing sophistication
3. HighLevel — best if you're building a broader white-label agency platform
4. Brevo — best if cost and simplicity dominate

If you're managing, say, 10–100+ Shopify clients, I'd lean Omnisend. If you tell me roughly how many clients you have, whether they're mostly Shopify, and whether you need white-labeling, I can narrow this down to the best platform and pricing model for an agency.

For your exact use case, Omnisend is probably the best fit if your clients are primarily Shopify/BigCommerce/WooCommerce ecommerce brands.

Omnisend lets you manage multiple stores, switch between them without logging in/out, reuse templates and workflows, and manage email, SMS and push within the same platform. It explicitly supports an agency/partner model where separate client accounts can retain their own ownership and billing while your agency users access them. Omnisend Omnisend Help Center

It also has a particularly useful Partner Portal + templated accounts feature: your agency can build automations, campaigns, signup forms, etc. once and copy them into client stores. Omnisend Help Center

omnisend.com

When I'd choose Klaviyo instead

Choose Klaviyo if your agency's competitive advantage is sophisticated ecommerce lifecycle marketing—complex segmentation, flows, personalization and revenue attribution.

Klaviyo now supports portfolios specifically for agencies, giving you a high-level view across multiple client accounts, and you can switch between multiple accounts with one login. help.klaviyo.com help.klaviyo.com

klaviyo.com

The downside is that it's more account-centric than agency-centric. Each ecommerce store generally has its own Klaviyo account, so the centralized experience isn't quite as purpose-built for an agency as an agency CRM platform. help.klaviyo.com

When I'd choose HighLevel

If you're not just doing ecommerce retention, but want your agency to provide CRM + email + SMS + automations + pipelines + lead management under one client-management system, HighLevel becomes very compelling.

It supports email and SMS directly, including bulk and scheduled SMS, within its client accounts.

For an agency managing multiple ecommerce clients and needing email + SMS from one interface, the best choice depends on whether you prioritize ecommerce performance or agency operations.

Best overall picks

My recommendation by agency type

If you are an ecommerce retention agency

Choose Klaviyo.

Best fit:

• Shopify/DTC brands
• abandoned cart, welcome, post-purchase, winback flows
• segmentation by customer behavior
• revenue reporting per client

The downside: it is more brand/account focused than agency dashboard focused, so managing dozens of clients can require good processes. Listicler

If you manage many different clients and want one login/dashboard

Choose GoHighLevel.

Best fit:

• 10–100+ client accounts
• white-label agency services
• client portals/reporting
• selling “email + SMS marketing” as a service

The tradeoff: for sophisticated ecommerce lifecycle marketing, Klaviyo usually has deeper ecommerce capabilities. Tool Decision Engine

If you are somewhere in the middle

A common agency stack is:

• Klaviyo per ecommerce client → best marketing results
• Agency SOPs + templates → easier scaling
• Optional agency management layer → client reporting and access control

Short answer

• Ecommerce-focused agency: Klaviyo
• General marketing agency managing many clients: GoHighLevel
• Shopify-heavy but simpler workflows: Omnisend
• Low-cost multi-client campaigns: Brevo

If you tell me roughly how many clients you manage (5, 50, 500) and whether they are mostly Shopify/DTC stores, I can narrow it down.

If you’re an agency managing email + SMS for multiple ecommerce clients, my first choice would be Klaviyo.

Why Klaviyo is probably the best fit

• One platform for email + SMS: campaigns, flows, segmentation, consent, profiles, and reporting can all live together rather than splitting email and SMS across tools. Subjectlime | Klaviyo Agency
• Multiple client accounts: Klaviyo lets you access and switch between multiple accounts from one login. Klaviyo Help Center
• Agency-level portfolio view: its Portfolios feature gives you a high-level view across multiple accounts, including performance/ROI comparisons. Klaviyo Help Center
• Ecommerce-native: particularly strong if your clients are Shopify/DTC brands.
• Agency-friendly permissions: you can have different access levels across client accounts. Klaviyo Help Center
• Shared billing is possible: for related accounts, Klaviyo can consolidate email/SMS usage under a shared billing arrangement, subject to approval. Klaviyo Help Center

How I'd rank the main options

Attentive is worth considering if your agency's work is heavily SMS-driven. It now combines SMS, email, RCS and push in one platform and emphasizes centralized omnichannel orchestration. Attentive

But for a typical agency managing 5, 10, 20+ Shopify stores, I'd start with Klaviyo because the multi-account/portfolio setup maps particularly well to the agency model.

help.klaviyo.com

If you tell me how many clients you manage (e.g. 10, 50, 100+) and whether they're mostly Shopify, I can narrow this down to the best 3 agency platforms and compare their pricing, white-label capabilities, client permissions, and reporting.

If you mean an agency managing email + SMS for multiple ecommerce brands, I’d narrow it to Klaviyo vs. GoHighLevel.

My pick: Klaviyo for ecommerce agencies

klaviyo.com is probably the strongest choice if your clients are primarily Shopify/DTC brands.

• Email + SMS are unified in the same customer profiles, segments, flows, and campaigns. Klaviyo Klaviyo Help Center
• Multi-account portfolios let an agency get a high-level view of multiple client accounts from one place. Klaviyo Help Center
• Excellent ecommerce-specific segmentation, abandoned-cart/post-purchase flows, revenue attribution, and Shopify ecosystem.
• Klaviyo now explicitly supports connecting multiple client accounts for agency workflows. Klaviyo Help Center

The important distinction: you still have separate client Klaviyo accounts, but the agency can manage/monitor them much more efficiently from a centralized view.

When I'd choose GoHighLevel instead

gohighlevel.com is better if your agency wants a true agency operating system, rather than an ecommerce retention platform.

It gives you:

• Multiple client sub-accounts
• Email + SMS
• CRM
• Automations
• Funnels/landing pages
• White-labeling
• Agency-level billing/reselling

So if your pitch is "we provide your entire marketing platform", HighLevel is compelling. If your pitch is "we grow your Shopify brand through email/SMS retention", I'd choose Klaviyo.

Quick decision

One caveat: If by "single interface" you literally mean one dashboard where your team can create campaigns, approve content, schedule sends, and report across 20–100 separate ecommerce clients without switching accounts, I'd look beyond the native platforms. There are newer agency layers that sit on top of multiple Klaviyo accounts specifically for this workflow. mailpanda.ai wizel.ai

If you tell me roughly how many clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, I can give you the best 3-platform shortlist and explain the pricing/agency setup.

If your agency primarily serves ecommerce/DTC brands, I’d pick Klaviyo.

Best fit: Klaviyo

Klaviyo is particularly strong when each client has their own Shopify/ecommerce store and you need to manage email + SMS, flows, segmentation, campaigns, and revenue attribution. Its Portfolio functionality gives agencies a single view across multiple client accounts, with account switching, reporting, permissions, and the ability to clone campaigns/flows/templates across accounts. Klaviyo Help Center Klaviyo

klaviyo.com

The big advantage is that Client A and Client B remain separate accounts, rather than dumping all clients into one database. That's much better for ecommerce agencies where each store has different customers, integrations, billing, and data. Klaviyo explicitly supports portfolios for agencies managing clients' brands. Klaviyo Help Center

When I'd choose HighLevel instead

HighLevel is arguably better if your priority is agency operations and white-labeling, rather than ecommerce-specific marketing depth.

It gives you client sub-accounts, email, SMS, CRM, unified inbox, automation, funnels, and white-label capabilities in one system. GoHighLevel GoHighLevel

gohighlevel.com

So I'd think about it this way:

My recommendation: If you're an ecommerce retention agency, use Klaviyo as the core platform. If you're a broader marketing/lead-gen agency that happens to serve ecommerce clients, HighLevel may be the better agency operating system.

One interesting option is using Klaviyo for the actual ecommerce email/SMS work and HighLevel for agency CRM/client operations, rather than forcing one tool to do everything.

If you mean one agency interface where your team can manage email + SMS for multiple ecommerce clients, I’d narrow it to Klaviyo vs. GoHighLevel, with the winner depending on what you’re optimizing for.

My pick for an ecommerce-focused agency: Klaviyo

Klaviyo is probably the best fit if your clients are primarily Shopify/DTC brands.

• Email + SMS in the same ecosystem
• Excellent ecommerce integrations and customer data
• Very strong segmentation, flows, attribution, and reporting
• You can connect multiple Klaviyo accounts to the same login and switch between them without logging in/out. Klaviyo Help Center
• Built specifically around ecommerce rather than being a generic agency CRM
• There is an official Klaviyo partner ecosystem for agencies. Klaviyo

The downside: you're still essentially managing separate client accounts, rather than having one giant shared workspace. For a retention/email-SMS agency, though, that's generally the right architecture.

My pick for a broader marketing agency: GoHighLevel

GoHighLevel is better if you want one agency operating system rather than primarily an ecommerce retention platform.

You get:

• Multiple client sub-accounts
• Email + SMS
• CRM
• Automations
• Funnels/websites
• Lead management
• White-labeling
• Agency-level management

That's where HighLevel has a major advantage: it was designed around the agency → multiple clients → sub-account model. Ecommerce Paradise

The tradeoff is that its ecommerce email/SMS functionality isn't as deep as Klaviyo's. For sophisticated Shopify segmentation, behavioral flows, and revenue attribution, Klaviyo is generally the stronger choice.

What about Omnisend?

Omnisend is worth considering if your agency has lots of smaller/mid-sized stores and you care about keeping costs and implementation complexity down.

It's ecommerce-native and combines email, SMS, and push. Its current offering also supports switching between multiple stores from one account, with support for up to 500 stores. Omnisend

The simple decision

If I were building an agency today specifically around email + SMS for ecommerce clients, I'd choose Klaviyo. The fact that you can access multiple client accounts from one login makes the multi-client workflow considerably easier, while retaining the ecommerce-specific data and automation depth. Klaviyo Help Center

If you tell me roughly how many clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can also compare Klaviyo vs GoHighLevel vs Omnisend specifically from an agency-owner perspective—including client management, pricing/margins, white-labeling, permissions, templates, reporting, and how easy it is to clone campaigns/flows across clients.

For an agency managing multiple ecommerce clients and needing email + SMS from one interface, the best choice depends on whether you prioritize ecommerce revenue performance or agency operations/white-label management.

Best overall options

My recommendation by agency type

If you are a Klaviyo/email retention agency

Choose Klaviyo.

Best when your service is:

• abandoned cart flows
• welcome sequences
• post-purchase campaigns
• segmentation
• lifecycle marketing
• Shopify/DTC growth

The downside: it is not as agency-native. You may manage many separate client accounts rather than one master operating dashboard. Listicler

If you are a full-service ecommerce agency

Choose GoHighLevel.

Best when you need:

• one login for many clients
• client sub-accounts
• white-label reporting
• CRM + SMS + email
• selling marketing automation as a productized service

The downside: it is generally less ecommerce-specialized than Klaviyo for deep Shopify lifecycle marketing. Tool Decision Engine

If you want the closest thing to a multi-brand command center

Look at agency-first platforms like Messaro or GoHighLevel. Messaro specifically emphasizes unlimited client workspaces, separate client environments, and switching between accounts from one dashboard. Messaro

A common agency stack

Many ecommerce agencies end up with:

• Klaviyo → client-facing email/SMS revenue engine
• Shopify integrations → customer/product/order data
• Agency reporting layer → dashboards and client reporting
• Project management tool → approvals and calendars

If your agency manages 10+ Shopify brands, I would usually lean Klaviyo + agency tooling rather than forcing everything into one platform. If your clients are broader (lead gen, services, ecommerce mixed), GoHighLevel becomes more attractive. Tool Decision Engine Listicler

A few questions would change the recommendation:

1. Are your clients mostly Shopify/DTC brands or mixed businesses?
2. Do you need white-label client logins?
3. Roughly how many client accounts do you manage (5, 50, 500)?

If you're an agency managing multiple ecommerce clients, I'd shortlist Omnisend and Klaviyo, with Omnisend probably the better fit if the priority is simplicity and managing many stores from one interface.

My pick: Omnisend

omnisend.com is particularly agency-friendly for this use case:

• Multiple stores/accounts: You can manage multiple client stores and switch between them without repeatedly logging in. Omnisend supports up to 500 stores under one account. Omnisend Omnisend Help Center
• Email + SMS together: Both channels are built into the same platform and automation workflows, rather than requiring separate tools. Omnisend
• Agency templates: Its Partner Portal lets agencies create reusable campaigns, automations, and signup forms and copy them to client stores. Omnisend Help Center
• Client separation: Each store retains its own contacts, automations, reports, and data, while your team can have different permissions per store. Omnisend Help Center
• Ecommerce-focused: It syncs products, orders, and customer data to power ecommerce-specific email/SMS automation. Omnisend Help Center

When I'd choose Klaviyo instead

klaviyo.com is the stronger choice if your agency works with larger/more sophisticated DTC brands and needs deeper segmentation, analytics, predictive features, and advanced lifecycle marketing.

Klaviyo also supports multiple client accounts under one login, and its Portfolio functionality provides a higher-level view across accounts. Klaviyo Help Center Klaviyo Academy It now has a unified omnichannel campaign builder for email, SMS, push, and WhatsApp as well. Klaviyo

Quick comparison

Bottom line: If you're saying "I want my team to log into one place, jump between 20–100 ecommerce clients, manage both email and SMS, reuse flows/templates, and keep client data separated," I'd start with Omnisend. Its current multi-store and Partner Portal features are unusually well aligned with that exact agency workflow. Omnisend Help Center Omnisend Help Center

If you tell me roughly how many clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can narrow this down to the best 2–3 options and compare agency pricing, white-labeling, permissions, reporting, and client billing.

If your agency mainly serves ecommerce brands, I’d pick klaviyo.com.

It’s probably the best fit when the requirement is specifically multiple ecommerce clients + email + SMS + centralized agency access.

My ranking

Why I'd choose Klaviyo

Klaviyo now supports multiple accounts under one login, and its Portfolio functionality gives agencies a high-level view across multiple brand accounts. Klaviyo Help Center Klaviyo Help Center

More importantly, it's built around ecommerce data: customer behavior, purchases, segments, flows, revenue attribution, etc. Its current omnichannel campaign builder can coordinate email, SMS, push and WhatsApp from one interface. Klaviyo

There is also shared billing for eligible groups of accounts, which can be useful when your agency is managing many clients. Klaviyo Help Center

When I'd choose HighLevel instead

If what you really mean by "single interface" is:

I want my agency team to log into one agency dashboard, jump between clients, manage email/SMS/CRM/funnels, white-label the software, and potentially resell it.

Then gohighlevel.com is the stronger choice.

HighLevel is explicitly structured around agency accounts + client sub-accounts, with agency-level permissions and centralized management. HighLevel Support Portal HighLevel Support Portal It also combines CRM, email, SMS, automation, funnels and white-labeling. GoHighLevel

The tradeoff is that Klaviyo is much more ecommerce/retention-centric, while HighLevel is more of an agency operating system.

The simple decision

• 90%+ Shopify/DTC/ecommerce clients → Klaviyo
• Mixed clients + lead generation + CRM + SMS → HighLevel
• Small/mid-sized Shopify clients where cost matters → Omnisend
• Complex B2B automation → ActiveCampaign

For a pure ecommerce marketing agency, I'd actually lean Klaviyo pretty strongly. Current comparisons also continue to identify Klaviyo as the stronger specialized choice for ecommerce agencies, while HighLevel wins on agency-native operations. Tool Decision Engine

If you tell me roughly how many clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, I can narrow this down to the best setup—including white-labeling, client billing, permissions, SMS costs, and reporting.

Klaviyo now supports multiple accounts under one login, and its Portfolio functionality gives agencies a high-level view across multiple brand accounts. Klaviyo Help Center Klaviyo Help Center

More importantly, it's built around ecommerce data: customer behavior, purchases, segments, flows, revenue attribution, etc. Its current omnichannel campaign builder can coordinate email, SMS, push and WhatsApp from one interface. Klaviyo

There is also shared billing for eligible groups of accounts, which can be useful when your agency is managing many clients. Klaviyo Help Center

When I'd choose HighLevel instead

If what you really mean by "single interface" is:

I want my agency team to log into one agency dashboard, jump between clients, manage email/SMS/CRM/funnels, white-label the software, and potentially resell it.

Then gohighlevel.com is the stronger choice.

HighLevel is explicitly structured around agency accounts + client sub-accounts, with agency-level permissions and centralized management. help.gohighlevel.com help.gohighlevel.com It also combines CRM, email, SMS, automation, funnels and white-labeling.

The tradeoff is that Klaviyo is much more ecommerce/retention-centric, while HighLevel is more of an agency operating system.

For an agency managing multiple ecommerce clients, I’d put Klaviyo at the top of the list.

Why it fits particularly well:

• Email + SMS in one platform: campaigns, automations/flows, segmentation, consent, and reporting can all work across both channels rather than maintaining separate email and SMS systems. Klaviyo Help Center Subjectlime | Klaviyo Agency
• Multiple client accounts: you can use one login to switch between separate client accounts. Klaviyo Help Center
• Portfolio view: Klaviyo's Portfolio feature gives agencies a higher-level view across multiple accounts, including usage and performance. Klaviyo Academy Klaviyo Help Center
• Good ecommerce fit: it has deep ecommerce integrations and is especially strong for Shopify/DTC businesses.
• Agency-friendly permissions: different users can have different permissions in different client accounts, which is useful when you have account managers, strategists, and execution teams. Klaviyo Help Center
• Shared billing is possible: for eligible related accounts, Klaviyo can consolidate email/SMS usage under a parent account. Klaviyo Help Center

How I'd rank the main options

Attentive is worth considering if your clients are large, SMS-heavy brands. It's particularly strong around SMS, conversational messaging, and omnichannel engagement, but Klaviyo tends to be the cleaner choice when you want email and SMS tightly integrated with ecommerce data. Attentive ATTN Agency

My recommendation: if you're building an agency stack today and most clients are Shopify/DTC, start with Klaviyo + its Portfolio/account-management capabilities. It gives you the closest thing to a centralized agency operating model while keeping each client's data and messaging environment separated.

If by "single interface" you mean literally one dashboard where your team can create/send campaigns for 20–100 different client stores without switching accounts, that's a slightly different requirement—and I'd evaluate agency-focused platforms differently.

For an agency managing multiple ecommerce clients, I’d narrow it to Klaviyo vs. Omnisend:

🥇 Best overall for an agency: Klaviyo

Klaviyo is probably the stronger choice if your clients are serious DTC/ecommerce brands.

• Email + SMS in the same platform and campaign builder. www.klaviyo.com
• You can use one login to switch between multiple client accounts. help.klaviyo.com
• Klaviyo now has agency-oriented capabilities for connecting and analyzing multiple client accounts, including cross-client reporting and audits. help.klaviyo.comsupport.omnisend.com
• Stronger choice if you're doing sophisticated segmentation, flows, attribution, testing, and lifecycle marketing.

🥈 Best if you prioritize agency efficiency: Omnisend

Omnisend is particularly interesting for agencies because its Partner Portal is explicitly built around managing client stores.

It supports:

• Multiple client stores from one login
• Email + SMS + push
• Reusable templates, campaigns, automations and segments
• Templated accounts, where you build an automation/campaign once and copy it to multiple client stores
• Store-specific permissions and billing
• Up to 500 stores under one account in its multi-store setup. support.omnisend.comsupport.omnisend.com

My recommendation

If you're building an agency where one team manages 10–100+ ecommerce brands, I'd seriously look at Omnisend first. Its current partner tooling is unusually aligned with that exact workflow. If your clients are larger brands where sophisticated CRM and revenue attribution matter more than operational simplicity, I'd lean Klaviyo. help.klaviyo.comsupport.omnisend.com

If you tell me roughly how many clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, I can also compare Klaviyo vs Omnisend vs Attentive specifically from an agency's perspective, including pricing, white-labeling, permissions, reporting, and client billing.

If you're an agency managing multiple ecommerce brands, and the key requirement is email + SMS from one interface across multiple client accounts, I’d narrow it to three:

My pick: Klaviyo if you're an ecommerce-specialist agency

Klaviyo is the strongest choice if your clients are primarily Shopify/WooCommerce/DTC brands. Its advantage is the depth of ecommerce data, segmentation, flows, product triggers, and revenue attribution, rather than simply being a communication platform. It supports both email and SMS. www.gohighlevel.com

The downside is that it isn't as agency-native as HighLevel—you don't get the same "one agency dashboard → isolated client subaccounts → white-label/resell" model.

Pick HighLevel if the agency experience matters most

HighLevel

HighLevel is probably the better answer if you mean:

"I want my team to log into one agency platform, switch between clients, manage email/SMS/CRM/automations, and potentially let clients access their own branded workspace."

It was designed around sub-accounts and agency management, with email, SMS, CRM, workflows, reporting and white-labeling in the same system. www.gohighlevel.com

The tradeoff is that Klaviyo is considerably more ecommerce-specialized.

Don't overlook Omnisend

Omnisend

This is particularly interesting if you're managing multiple ecommerce stores. Omnisend explicitly supports multiple stores under one account, lets you switch between them without logging in/out, reuse templates/workflows, and manage email, SMS and push together. www.omnisend.com

Bottom line

• Ecommerce retention agency → Klaviyo
• Full-service agency / white-label SaaS → HighLevel
• Lots of ecommerce stores + simple centralized email/SMS → Omnisend

If your real requirement is "50+ ecommerce clients, one agency login, client-level permissions, reusable campaigns/flows, consolidated reporting, and ideally white-label", I'd evaluate HighLevel vs. Omnisend vs. Klaviyo's agency/partner setup specifically rather than generic email platforms.

For an agency managing multiple ecommerce clients, I’d put Omnisend at the top of the list right now.

My ranking

🥇 Omnisend — probably what you're looking for

Omnisend is unusually well suited to an agency model. You can manage multiple stores from one account, switch between them without repeatedly logging in, control user permissions by store, and reuse templates/workflows across stores. It supports email, SMS and push from the same platform. www.omnisend.comsupport.omnisend.comhelp.klaviyo.com

More importantly for an agency, Omnisend added a Partner Portal with templated accounts. You can build campaigns, automations and signup forms once and copy them into multiple client stores—very useful if you're onboarding lots of Shopify/WooCommerce/BigCommerce clients. support.omnisend.com

Omnisend

🥈 Klaviyo — better if your clients are more sophisticated

Klaviyo is arguably the stronger choice if you're managing higher-value Shopify brands that need deep segmentation, sophisticated customer data, advanced attribution, and complex automations.

Klaviyo supports multiple accounts under one login, so an agency can switch between client accounts without logging in and out. Its current omnichannel builder also combines email, SMS, push and WhatsApp in a single campaign interface. help.klaviyo.com

Klaviyo

The downside is that Klaviyo is more expensive/complex, and each ecommerce store generally needs its own Klaviyo account. help.klaviyo.com

🥉 Attentive — if SMS is the core service

Attentive is particularly strong when you're selling SMS marketing as a major agency service. It now combines SMS, email, RCS and push and has strong conversational/SMS capabilities. www.attentive.com

Attentive

But for a typical ecommerce agency doing email + SMS + flows + campaigns across lots of Shopify stores, I'd generally choose Omnisend or Klaviyo first.

What I'd choose

If you're building an agency today:

• 5–30 smaller/mid-market ecommerce clients → Omnisend
• Higher-end Shopify/DTC clients → Klaviyo
• Agency specializes heavily in SMS → Attentive
• Need CRM/sales/support beyond ecommerce marketing → HubSpot

The particularly compelling thing about Omnisend for an agency is that it isn't merely "multiple accounts under one login." Its Partner Portal and templated-account functionality are explicitly designed around agencies replicating campaigns and automations across client stores. support.omnisend.com

If you tell me roughly how many clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can compare Omnisend vs Klaviyo specifically from an agency owner's perspective—pricing, client permissions, white-labeling, reporting, templates, SMS costs, and margins.

For an agency managing email + SMS for multiple ecommerce clients, I’d put Klaviyo first.

My ranking

Why Klaviyo: it is designed around a 1:1 relationship between an ecommerce store and an account, but agencies can manage multiple accounts with one login. Its Portfolio gives you a centralized view across accounts, including performance, billing, users, and usage. help.klaviyo.com

It also supports email and SMS in the same account, with sophisticated segmentation, flows, customer profiles, and ecommerce integrations. For an agency, that makes it particularly strong when you're running things like:

• Welcome flows
• Abandoned cart/browse
• Post-purchase
• Winback
• Promotional campaigns
• Email/SMS orchestration
• Client-level reporting
• Multiple Shopify stores

There is even a shared-billing option for linked Klaviyo accounts, although it's subject to approval and has account-family limits. help.klaviyo.com

When I'd choose Attentive instead

If your agency is SMS-first and works with larger/enterprise ecommerce brands, I'd seriously consider Attentive. It now combines SMS, email, RCS and push, and has a dedicated agency partner program with partner managers, training, revenue-share opportunities, and support. www.attentive.com

The important distinction

If by "single interface" you mean:

"I want one login/dashboard where my team can see and operate every client's campaigns, rather than having to jump between completely separate client accounts."

Then Klaviyo is good, but it isn't truly one universal workspace. Each ecommerce client generally has its own Klaviyo account, with Portfolio providing the agency-level layer on top. academy.klaviyo.com

If you're building an agency and want 10–100+ ecommerce clients under one operational interface, I'd evaluate the platforms specifically on multi-account permissions, client separation, white-label reporting, reusable templates/flows, billing, and whether your team can send on behalf of clients without constantly switching contexts.

If you tell me roughly how many clients you manage (e.g. 5, 20, 100+) and whether they're mostly Shopify, I can narrow this down to the best 2–3 options and compare their agency pricing + multi-client workflow.

For an agency managing email + SMS for multiple ecommerce clients, I’d put Klaviyo at the top of the list—especially if most clients are on Shopify.

My ranking

1. Klaviyo — best overall

Klaviyo is probably the best fit if your agency wants one standardized system across many Shopify clients. You can use a single login to access multiple separate client accounts, switch between them, manage permissions, and—on paid plans—use a portfolio for a higher-level view. It also supports copying flows, forms, segments and templates between accounts, which is particularly useful for an agency building repeatable client playbooks. help.klaviyo.com

It also has a unified email/SMS campaign builder, so your team isn't managing two disconnected systems. www.klaviyo.com

2. Attentive — better for larger, SMS-heavy clients

I'd consider Attentive when your clients are larger ecommerce brands and SMS is a major revenue channel. It's particularly strong around SMS, conversational messaging, identity resolution and managed/enterprise support, while now offering email in the same platform. www.attentive.com

The tradeoff is that it's generally more enterprise-oriented, so I wouldn't make it the default platform for every smaller agency client.

3. Yotpo — don't choose it for this anymore.

Yotpo exited SMS/email and named Attentive its preferred SMS/email partner, so older recommendations of Yotpo as an email+SMS platform are now outdated. www.attentive.com

What I'd do if I were building the agency

Use Klaviyo as the default client platform.

Structure it roughly like:

Agency
→ Client A Klaviyo account
→ Client B Klaviyo account
→ Client C Klaviyo account
→ Client D Klaviyo account

Then build a standardized library of:

• Welcome flows
• Abandoned cart
• Browse abandonment
• Post-purchase
• Winback
• Email campaigns
• SMS campaigns
• Segments
• Templates
• Reporting dashboards

The big advantage is that you can reuse the agency's proven flows across stores rather than rebuilding everything client-by-client. help.klaviyo.com

If you tell me roughly how many clients you manage (e.g. 5, 20, 100+) and whether they're mostly Shopify, I can narrow this down further—including which platform has the best agency/multi-client workflow and pricing model.

For an agency managing multiple ecommerce clients, I’d put Omnisend at the top of the list right now—especially if your clients are mostly Shopify, WooCommerce, or BigCommerce stores.

My ranking

Why Omnisend stands out: it explicitly supports agencies/partners managing multiple stores. You can switch between client stores from one login, control permissions by store, and reuse templates, automations, and segments. Omnisend says its multi-store setup can support up to 500 stores under one account. support.omnisend.com

More importantly for an agency, Omnisend introduced templated accounts in 2026: you can build campaigns, automations, and signup forms once and copy them into multiple client stores. support.omnisend.com

When I'd choose Klaviyo instead

Choose Klaviyo if your clients are larger DTC brands and you need deeper segmentation, analytics, predictive capabilities, and more sophisticated customer-data work.

Klaviyo also lets you use one login to switch among multiple client accounts, and its Portfolio functionality gives agencies a higher-level view across accounts. However, each ecommerce store generally remains a separate Klaviyo account rather than multiple stores living inside one account. help.klaviyo.com

The key distinction

If your agency's workflow is:

Client A → Client B → Client C → Client D → same dashboard → reuse flows/templates → send both email + SMS

I'd pick Omnisend.

If it's:

Client A → complex data/segmentation → advanced attribution → large contact database → sophisticated lifecycle marketing

I'd pick Klaviyo.

And if you're specifically building an SMS-first agency, I'd also evaluate Attentive, which now combines SMS, email, RCS, and push in one platform. www.attentive.com

Bottom line: Omnisend is probably the best operational fit for a multi-client ecommerce agency; Klaviyo is the better choice when sophistication matters more than agency simplicity.

If you tell me roughly how many clients you manage (e.g. 10, 50, 200+) and whether they're mostly Shopify, I can narrow this down to the best platform—including agency pricing, client permissions, white-labeling, and reporting.

If you're an agency managing multiple ecommerce clients, I'd narrow it to Klaviyo vs. Omnisend, rather than a general agency CRM like GoHighLevel.

My pick: Klaviyo

Klaviyo is probably the best fit if your clients are primarily Shopify/ecommerce brands and you're doing serious retention marketing.

Why:

• Email + SMS in one platform, including coordinated multi-channel campaigns. www.klaviyo.com
• Excellent ecommerce segmentation, flows, customer profiles, and revenue attribution.
• Strong Shopify ecosystem and a large agency/partner ecosystem.
• Better choice when clients have sophisticated lifecycle marketing needs or significant revenue flowing through email/SMS. ecommerce-times.com

The sleeper choice: Omnisend

Omnisend is especially interesting for an agency because it has multi-store management built in. You can switch between stores from one account, reuse templates/workflows, and manage email, SMS, and push across stores. www.omnisend.com

Its Partner Portal also lets agencies create templated accounts and copy campaigns, automations, and signup forms into client stores—which is genuinely useful if you're onboarding lots of similar ecommerce clients. support.omnisend.com

Where GoHighLevel fits

HighLevel is arguably better if your priority is agency operations rather than ecommerce retention specifically. It gives you sub-accounts, CRM, email, SMS, automation, funnels, reporting, and white-labeling. Its Unlimited plan advertises unlimited sub-accounts. www.gohighlevel.com

But I'd hesitate to make it the core platform for a specialized ecommerce retention agency. Klaviyo's ecommerce data/segmentation and attribution are generally more appropriate.

Quick decision

If you tell me roughly how many clients you manage (e.g. 10, 50, 200), whether they're mostly Shopify, and whether you want to resell the platform under your agency's brand, I can tell you which one I'd pick and how I'd structure the accounts.

For an agency managing multiple ecommerce clients, I’d put Klaviyo at the top of the list—especially if most clients are Shopify/DTC.

Best overall: Klaviyo

Klaviyo

Why it fits agencies well:

• Email + SMS in one platform with shared customer profiles, segmentation, flows, and attribution. www.klaviyo.com
• Strong ecommerce integrations, particularly with Shopify.
• You can build flows that mix email and SMS rather than managing separate automation systems.
• Good fit for repeating an agency's playbooks—welcome, abandoned cart, browse abandonment, post-purchase, winback, etc.—across many brands.
• Its omnichannel campaign builder now supports coordinating multiple messages/channels from one visual interface. www.klaviyo.com

The important caveat: Klaviyo isn't really a "single master dashboard where an agency operates every client's account as one account." You'll generally be managing separate client accounts/workspaces. So if by "single interface" you mean one login/workspace that centrally controls 20–100 independent client stores, I'd evaluate the agency/multi-account workflow specifically rather than just the messaging features.

Strong alternative: Attentive

Attentive

I'd consider Attentive when your clients are larger, SMS-heavy ecommerce brands. It now combines email and SMS and emphasizes unified customer profiles and cross-channel campaigns. www.attentive.com

The tradeoff is that it's generally more enterprise/SMS-oriented and tends to involve a more managed sales/service model.

Interesting option: Yotpo SMS & Email

Yotpo has useful multi-store functionality—for example, its documentation specifically describes copying flows between stores, which could be attractive to an agency operating standardized client playbooks. support.yotpo.com

However, there's an important wrinkle: Yotpo announced Attentive as its preferred SMS/email partner after exiting that part of its business, so I wouldn't make Yotpo my first choice for a new agency-wide messaging stack in 2026. www.attentive.com

My recommendation by agency type

If you tell me roughly how many clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, WooCommerce, or mixed, I can narrow this down to the best 2–3 platforms specifically for an agency operating multiple client accounts.

For an agency managing multiple ecommerce clients and needing email + SMS from one interface, the best choice depends on whether you want an agency operating system or an ecommerce retention platform.

Best overall for an ecommerce agency: Klaviyo

Best if your clients are mostly Shopify/DTC brands.

Why agencies like it:

• Excellent ecommerce segmentation (purchase history, LTV, churn risk, browsing behavior)
• Strong email + SMS flows (welcome, abandoned cart, winback, post-purchase)
• Revenue attribution that clients understand
• Large ecommerce ecosystem and partner network sweatpantsagency.com

Downside: It is built around the brand account more than the agency dashboard. Managing dozens of clients can require process discipline.

Best for a true multi-client agency dashboard: HighLevel

Best if you want to sell “marketing systems” rather than just email/SMS.

Strengths:

• Separate client sub-accounts
• White-label options
• Centralized management
• Built-in CRM, funnels, email, SMS, automations tooldecisionengine.com

Downside: Ecommerce lifecycle marketing is not as deep as Klaviyo (especially segmentation and Shopify revenue analytics).

Best budget-friendly ecommerce option: Omnisend

Good for smaller Shopify/WooCommerce stores.

Strengths:

• Email + SMS together
• Ecommerce-focused automations
• Easier onboarding for smaller clients
• Agency partner ecosystem partnerpage.omnisend.com

Downside: Less sophisticated than Klaviyo for large DTC brands.

Best if you manage many small clients and need simple billing: Brevo

Good for agencies serving local businesses or smaller stores.

Strengths:

• Email + SMS + WhatsApp options
• More cost-conscious pricing model
• Easier for simple campaigns marketing-software-review.com

Downside: Less ecommerce-specific intelligence.

My recommendation by agency model

A common setup for serious ecommerce agencies is:

• HighLevel for agency CRM, pipelines, client management, reporting
• Klaviyo inside each ecommerce brand account for revenue-driving email/SMS

If you tell me roughly how many clients you manage (5, 50, 500) and whether they are mostly Shopify stores, I can narrow it down.

If you mean an agency managing email + SMS for multiple ecommerce brands from one agency-level interface, I’d narrow it to Klaviyo vs. HighLevel.

My pick: Klaviyo for ecommerce agencies

Klaviyo is probably the best fit if your clients are primarily Shopify/DTC brands.

• Built around ecommerce data — customer events, purchases, product data, segmentation, flows, and revenue attribution are major strengths.
• Email + SMS are native channels, including coordinated omnichannel campaigns. www.klaviyo.com
• Multiple client accounts: one login can access multiple Klaviyo accounts, and its Portfolio feature provides a consolidated view across accounts. help.klaviyo.comhelp.klaviyo.com
• You can keep each client's data, billing, permissions, and ecommerce integration separated rather than dumping every client into one database.
• Klaviyo is specifically positioning its newer agency tooling around managing multiple client accounts and cross-client reporting. help.klaviyo.com

Klaviyo

When I'd choose HighLevel instead

HighLevel is better if your agency wants one broader operating system rather than primarily an ecommerce retention platform.

Its agency architecture is excellent: you have an agency account with separate client sub-accounts, permissions, CRM, automations, email, SMS, funnels, etc. help.gohighlevel.comhelp.klaviyo.com

That makes HighLevel particularly attractive if you're selling something like:

"We run your CRM + email + SMS + lead capture + automation."

But for serious ecommerce retention, I'd generally favor Klaviyo because of its deeper ecommerce segmentation, flows, and revenue attribution. tooldecisionengine.com

HighLevel

Quick decision

One important distinction: if by "single interface" you mean literally one dashboard where your team can see and operate all clients without switching into individual client accounts, I'd look more closely at the agency/portfolio capabilities before choosing. Klaviyo's Portfolio gives you centralized account management and reporting, while HighLevel's sub-account architecture is more explicitly agency-first. help.gohighlevel.comhelp.klaviyo.com

If you tell me how many ecommerce clients you manage (e.g. 10, 50, 200) and whether they're mostly Shopify, I can give you a much more specific recommendation, including pricing, white-labeling, client permissions, SMS costs, and reporting.

If you’re an agency managing multiple ecommerce clients, I’d narrow it to HighLevel vs. Klaviyo:

🥇 Best agency operating system: HighLevel

HighLevel is probably the best fit if your priority is one agency interface for many client accounts.

• Separate sub-accounts for each client
• Agency-level user management and permissions help.gohighlevel.com
• Email + SMS in the same platform help.gohighlevel.com
• Centralized agency controls for email services help.gohighlevel.com
• White-label agency experience
• Client billing/rebilling capabilities
• Particularly good if your agency also handles CRM, lead follow-up, appointment workflows, and conversational SMS

HighLevel is designed around the agency → multiple clients model rather than treating each brand as an isolated marketing account.

🥇 Best ecommerce marketing platform: Klaviyo

Klaviyo is stronger if your agency's core service is ecommerce retention/CRM rather than broader client management.

It supports email + SMS and lets you manage multiple client accounts from one login, with portfolios providing a higher-level view across accounts. help.klaviyo.com

Its big advantage is ecommerce sophistication: segmentation, product/event data, automated flows, revenue attribution, and deep Shopify integration.

My recommendation

The key distinction: HighLevel is better at running an agency, while Klaviyo is better at running ecommerce lifecycle marketing.

If you tell me how many clients you have, whether they're mostly Shopify, and whether you need white-labeling, I can recommend the best setup—including HighLevel vs Klaviyo vs Omnisend vs Attentive and what the approximate monthly cost would look like.

If you're an agency managing multiple ecommerce clients and need both email + SMS from one place, I'd narrow it to two:

My pick: Klaviyo for ecommerce agencies

Klaviyo is probably the better fit if your clients are primarily Shopify/DTC brands. It is built around ecommerce data, segmentation, flows, revenue attribution, and coordinated email/SMS campaigns. Its Portfolio functionality gives agencies a consolidated view across multiple client accounts, while allowing separate accounts and permissions for each client. www.klaviyo.comhelp.klaviyo.com

It also supports using one login to access multiple Klaviyo accounts, which is useful when each ecommerce client needs its own data environment. help.klaviyo.com

Klaviyo

When I'd choose HighLevel instead

HighLevel makes more sense if you're not just doing ecommerce retention—you want an agency operating system with client sub-accounts, CRM, pipelines, automations, email, SMS, forms, funnels, and potentially white-labeling. Its agency/sub-account structure is explicitly designed for managing users across multiple client accounts. help.gohighlevel.com

HighLevel

Rule of thumb:

• 🛍️ 80%+ Shopify/ecommerce clients → Klaviyo
• 🏢 Mixed clients + CRM/lead gen + SMS → HighLevel
• 📈 Agency's core service is increasing ecommerce revenue through email/SMS → Klaviyo
• ⚙️ Agency wants one white-labeled platform clients can log into → HighLevel

One important distinction: "single interface" doesn't necessarily mean one shared client database. With Klaviyo, you generally maintain a separate account per ecommerce store, but manage those accounts through a consolidated portfolio/login. That's actually preferable for agencies because client data and permissions stay isolated. www.klaviyo.comhelp.klaviyo.com

If you tell me how many clients you have (e.g. 10, 50, 200) and whether they're mostly Shopify, I can give you a more specific recommendation, including pricing and agency/multi-account limitations.