ChatGPT answers, unedited

For an agency managing multiple ecommerce shops on a tight budget, I’d shortlist Omnisend first, Klaviyo second.

My pick: Omnisend

Omnisend is particularly well suited to your setup because you can manage multiple stores from one account, switch between them, control team permissions, and copy templates/workflows/segments between stores. It supports up to 500 stores under one account. Each store is still billed separately, though, based on its own contact count. support.omnisend.com

The current pricing is also attractive for budget-conscious agencies:

• Free: 250 contacts / 500 emails per month
• Standard: starts at $16/mo, but SMS isn't available for new subscribers on this tier
• Pro: starts at $59/mo, with SMS available as an add-on starting around $0.007/SMS in the US/Canada. support.omnisend.com

That makes Omnisend my choice if you're managing lots of smaller Shopify/WooCommerce stores and don't need extremely sophisticated customer-data modeling.

When I'd choose Klaviyo instead

Klaviyo is better if your agency is doing sophisticated lifecycle marketing—complex segmentation, advanced flows, predictive analytics, and heavy Shopify customization.

It has good multi-account functionality: one login can switch between multiple client/store accounts. More importantly for an agency, Klaviyo has shared billing, where related accounts can potentially draw from one pooled email/SMS allowance. Klaviyo says this can support one parent plus up to 33 child accounts, although shared billing requires approval from Klaviyo Support. help.klaviyo.com

The catch is cost. Once client lists get large, Klaviyo can become substantially more expensive than Omnisend.

What I'd do for an agency

One important caveat: neither platform gives you one giant shared audience across unrelated client stores—and you generally don't want that anyway. Each client should have isolated customer data, sending domains, consent records, automations, etc. The useful "shared" layer is your agency's users, templates, processes, and account management.

If you tell me roughly how many shops you manage, average contacts per shop, whether they're Shopify/WooCommerce/etc., and approximate monthly email + SMS volume, I can work out which setup is likely to be cheapest—including Omnisend vs Klaviyo vs Brevo vs MailerLite.

If you’re an agency managing multiple ecommerce stores, I’d optimize for three things: multi-store management, reusable campaigns/flows, and low cost per store.

My shortlist

1. Omnisend — probably your best fit

I'd start here for a budget-conscious agency.

Omnisend is specifically designed for ecommerce and lets you manage multiple stores from one account, switch between them, and reuse templates/workflows across stores. It also combines email, SMS and push rather than requiring separate tools. Omnisend Omnisend Help Center

The big caveat is that each store has its own subscription, so you don't literally get one cheap subscription covering all your clients. Omnisend Help Center

Current pricing starts at $16/month for Standard and $59/month for Pro. For new subscribers, SMS requires Pro, with SMS pricing starting at $0.007/message in the US/Canada. Omnisend Help Center Omnisend Help Center

For an agency, the killer feature is build once, reuse across stores. You could create standardized flows such as:

• Welcome series
• Abandoned cart
• Browse abandonment
• Post-purchase
• Win-back
• VIP/customer loyalty
• SMS promotion
• Back-in-stock

Then clone/adapt them for each client.

omnisend.com

2. Klaviyo — better if clients have serious revenue

Klaviyo is what I'd use when a client's ecommerce operation is large enough that segmentation, attribution and sophisticated lifecycle marketing justify the additional cost.

It supports multiple accounts under one login, which is useful for an agency managing several brands. Klaviyo Help Center It also has a shared-billing/account-family feature that can pool email and SMS usage across related accounts, although you have to request it from Klaviyo and approval is case-by-case. One account family can have a parent plus up to 33 child accounts. Klaviyo Help Center

That could actually be very interesting for your agency if you have several related stores and enough combined volume.

Klaviyo's free tier currently covers up to 250 profiles and 500 emails/month, plus $5/month of mobile messages. Klaviyo

I'd therefore think of Klaviyo as your premium client tier, rather than putting every small client on it.

3. Mailchimp — only if SMS isn't central

Mailchimp can make sense for clients who mostly need newsletters, basic automations and straightforward campaigns.

But if your selling point to clients is "we manage your ecommerce email + SMS lifecycle marketing," I'd lean Omnisend or Klaviyo. Ecommerce-specific automation is where those platforms make more sense.

What I'd actually do as an agency

I'd create two service tiers:

Starter clients → Omnisend

Use standardized, agency-owned templates and flows. Keep the setup highly repeatable so you're not spending five hours rebuilding the same abandoned-cart sequence for every store.

Larger clients → Klaviyo

Use it when the client has enough traffic/revenue that advanced segmentation, predictive analytics, attribution and more sophisticated customer journeys can pay for themselves.

One particularly attractive setup is to investigate Klaviyo shared billing for clients that are sufficiently related; otherwise, Omnisend's multi-store setup is probably simpler operationally. Klaviyo Help Center

If I were starting your agency today on a tight budget, I'd pick Omnisend first. Its multi-store workflow/template reuse is unusually well aligned with an agency model, while the email + SMS combination keeps your tech stack small. Omnisend Omnisend Help Center

If you tell me roughly how many shops you manage, average contacts per shop, and whether they're mostly Shopify/WooCommerce/BigCommerce, I can work out which setup is likely to be cheapest and what I'd charge each client.

For an agency managing multiple ecommerce shops on a tight budget, I’d shortlist these:

1. Omnisend — my recommendation

Omnisend is unusually well suited to your situation. You can manage multiple stores from one account, switch between them, reuse templates/workflows, and control team access by store. Each store still has its own data and subscription, which is important for keeping client accounts separated. Omnisend Help Center Omnisend Help Center

More importantly for an agency, Omnisend added a Partner Portal and templated accounts in 2026. You can build a library of campaigns, automations and signup forms once, then copy them into client stores. Omnisend Help Center Omnisend Help Center

Its current Pro plan starts around $59/month list price, with unlimited email and SMS available as an add-on; the current pricing page is showing promotional pricing as well. Omnisend Help Center Omnisend

Why I'd choose it: you're paying for an ecommerce-focused platform rather than a general marketing platform, and the multi-store/template functionality directly attacks the biggest agency cost: repetitive setup.

2. Klaviyo — better if sophistication matters more than price

Klaviyo is probably the stronger choice if your clients need sophisticated segmentation, reporting, predictive analytics, and complex lifecycle marketing.

It supports multiple accounts under one login and has Portfolios for viewing/managing multiple brand accounts. Klaviyo Help Center Klaviyo Help Center

There's also a particularly interesting option for an agency: shared billing can pool email/SMS usage across related Klaviyo accounts. It's not automatically available—you have to request it from Klaviyo, and approval is case-by-case. Klaviyo Help Center

The downside is cost. For a budget-conscious agency with lots of small stores, I'd only move to Klaviyo when a client's revenue/complexity justifies it.

3. Sendlane — worth testing

I'd put Sendlane on the shortlist if you want something more agency-oriented than a basic email tool but don't need all of Klaviyo's sophistication.

That said, I wouldn't make it your default without pricing out your actual client portfolio. With 10–20+ stores, the multi-account economics matter much more than the headline monthly price.

What I'd do in your shoes

I'd standardize the agency around Omnisend and create a reusable "agency playbook":

• Welcome series
• Abandoned cart
• Browse abandonment
• Post-purchase
• Win-back
• Product replenishment
• VIP/customer segments
• Promotional campaign templates
• SMS opt-in + abandoned-cart SMS
• Basic reporting dashboard

Then use Omnisend's templated-account functionality to clone the proven setup into each new Shopify/WooCommerce/BigCommerce client. Omnisend Help Center

One important caveat: you don't actually get one shared subscription across all stores. Each Omnisend store has its own subscription and is billed according to its contact count. What you consolidate is the agency's management, users, templates, workflows and operational overhead. Omnisend Help Center

If you tell me roughly how many shops you manage (e.g. 5, 20, 50), average contacts per shop, and whether they're mostly Shopify, I can work out which setup is likely to be cheapest and compare the approximate monthly cost of Omnisend vs. Klaviyo for your agency.

Why I'd choose it: you're paying for an ecommerce-focused platform rather than a general marketing platform, and the multi-store/template functionality directly attacks the biggest agency cost: repetitive setup.

2. Klaviyo — better if sophistication matters more than price

Klaviyo is probably the stronger choice if your clients need sophisticated segmentation, reporting, predictive analytics, and complex lifecycle marketing.

It supports multiple accounts under one login and has Portfolios for viewing/managing multiple brand accounts. Klaviyo Help Center Klaviyo Help Center

There's also a particularly interesting option for an agency: shared billing can pool email/SMS usage across related Klaviyo accounts. It's not automatically available—you have to request it from Klaviyo, and approval is case-by-case. Klaviyo Help Center

The downside is cost. For a budget-conscious agency with lots of small stores, I'd only move to Klaviyo when a client's revenue/complexity justifies it.

3. Sendlane — worth testing

I'd put Sendlane on the shortlist if you want something more agency-oriented than a basic email tool but don't need all of Klaviyo's sophistication.

That said, I wouldn't make it your default without pricing out your actual client portfolio. With 10–20+ stores, the multi-account economics matter much more than the headline monthly price.

What I'd do in your shoes

I'd standardize the agency around Omnisend and create a reusable "agency playbook":

• Welcome series
• Abandoned cart
• Browse abandonment
• Post-purchase
• Win-back
• Product replenishment
• VIP/customer segments
• Promotional campaign templates
• SMS opt-in + abandoned-cart SMS
• Basic reporting dashboard

Then use Omnisend's templated-account functionality to clone the proven setup into each new Shopify/WooCommerce/BigCommerce client.

For an agency managing multiple ecommerce shops on a tight budget, I’d prioritize platforms that let you:

• manage multiple brands/workspaces cleanly
• reuse flows/templates
• keep client data separated
• avoid paying enterprise pricing per store
• handle both email + SMS in one place

My shortlist:

My recommendation for your situation

Default agency stack: Omnisend

• Create one agency account.
• Add each shop as its own store/workspace.
• Build reusable templates:
  • welcome series
  • abandoned cart
  • browse abandonment
  • post-purchase
  • winback
  • VIP/customer segments
• Charge clients a monthly management fee + platform pass-through.

It’s probably the best balance of cost, ecommerce features, and operational simplicity for many small shops. www.omnisend.comecommerce-times.com

When I’d use Klaviyo instead

Use Klaviyo per client if:

• the store is doing meaningful volume (e.g., six figures/month)
• segmentation matters heavily
• you need detailed attribution reporting
• you’re running sophisticated lifecycle marketing

Klaviyo tends to win once the client’s retention program is a major revenue channel. ecommerce-times.com

Agency workflow I’d avoid

I would avoid putting all clients into one shared customer database. Even if the software technically allows it, it creates problems with:

• customer data ownership
• unsubscribes
• reporting
• client offboarding
• compliance

Better model:

• agency owns the master login/admin relationship
• each client has a separate store/account
• you standardize templates and processes across them

A couple questions would change the recommendation:

1. Are these mostly Shopify, WooCommerce, BigCommerce, or mixed?
2. Roughly how many shops (5, 20, 100+)?
3. Do clients pay you for the software, or are you trying to absorb the cost into your retainer?

For an agency managing multiple ecommerce shops on a tight budget, I’d shortlist these:

1. Omnisend — my pick

This is probably where I'd start.

Omnisend explicitly supports multiple stores under one account, letting your team switch between stores without separate logins. You can also copy templates, workflows and segments between stores, while keeping each shop's customer data and reporting separate. It supports up to 500 stores under one account. support.omnisend.com

The important caveat for an agency: each store still has its own subscription, so you're not getting one magical unlimited agency license. But centralized users, billing, and management make it much less painful operationally. support.omnisend.comhelp.klaviyo.comhelp.klaviyo.com

Pricing is particularly attractive for small shops: Standard starts at $16/month, while Pro starts at $59/month and is the tier that currently includes SMS for newer subscriptions. SMS starts at $0.007/message according to Omnisend's current pricing information. support.omnisend.com

Why I'd choose it for an agency: you can build a master set of ecommerce flows—welcome, abandoned cart, browse abandonment, post-purchase, win-back, etc.—and replicate them across clients rather than rebuilding everything.

2. Klaviyo — best if clients can afford it

Klaviyo is the more sophisticated option, particularly if you're doing serious segmentation, predictive analytics and highly customized automation.

Its newer Portfolios feature is specifically designed for managing multiple brand accounts, including client brands for agencies, with a high-level view of performance, billing, users and data. Portfolios themselves don't add a fee. help.klaviyo.com

The downside for your situation is cost. You're paying for each client's Klaviyo account, and SMS is an additional usage-based cost. help.klaviyo.com

I'd use Klaviyo when the client's revenue justifies the extra sophistication, rather than making it your default platform for every small shop.

3. Sendlane — worth considering for volume

Sendlane is interesting if your agency eventually gets into larger sending volumes. Its pricing model is based on send volume rather than profiles, with unlimited contacts, and SMS starts at $0.009/credit including carrier fees. www.sendlane.com

But for a collection of small ecommerce stores, I'd generally favor Omnisend because its entry-level economics are much friendlier.

What I'd actually do

I'd standardize your agency around Omnisend and create a reusable "agency playbook":

• Core flows: welcome → abandoned cart → browse abandonment → post-purchase → win-back
• Reusable templates: 10–20 proven campaign designs
• Reusable segments: VIP, recent purchasers, engaged subscribers, lapsed customers
• SMS: reserve for high-value events rather than blasting every campaign
• Client separation: each store gets its own data, reporting and billing
• Agency account: your team gets centralized access and can move between clients

That gives you a fairly scalable setup without forcing a $500+/month marketing stack onto every tiny client.

One particularly useful feature is that Omnisend lets agencies keep separate client accounts while having the same agency users access them, and explicitly recommends that model for partners/agencies when clients need separate ownership and billing. support.omnisend.com

Bottom line:
Omnisend for most clients → Klaviyo when a client grows into it → Sendlane if your agency becomes particularly volume-heavy.

If you tell me roughly how many shops you manage, average subscriber count per shop, and whether they're Shopify/WooCommerce/etc., I can work out which setup would be cheapest and what the approximate monthly software cost would be.

For an agency managing multiple ecommerce stores on a tight budget, I’d shortlist these three:

1. Omnisend — my pick for an agency

This is probably where I'd start.

Omnisend explicitly supports multiple stores under one account, letting your team switch between stores without logging in/out. More importantly for an agency, you can reuse email templates and workflows across stores, which can eliminate a lot of repetitive setup. Email, SMS, and push are also handled in the same platform. www.omnisend.com

The big caveat: each store has its own subscription, so you don't literally get one cheap plan covering every client's contacts. support.omnisend.com

For current pricing, Omnisend's Standard plan starts around $11.20/month in the pricing interface for 500 contacts, while Pro is currently positioned as the plan that includes SMS for newer paid subscribers. SMS pricing starts at $0.007/message at high US volume. www.omnisend.com

Why I'd choose it: your agency can build a proven abandoned-cart/welcome/post-purchase/etc. framework once, then replicate it across clients.

2. Klaviyo — best if clients are more sophisticated

Klaviyo is the one I'd choose if you're managing higher-revenue stores where segmentation, attribution, automation and analytics matter more than software cost.

It supports multiple accounts under one login, and paid users can create portfolios to get a consolidated view across accounts. You can also clone flows, campaigns, segments and templates between accounts. help.klaviyo.com

There's an especially interesting option for an agency: Klaviyo has shared billing that can combine up to 20 accounts under one billing family, with a shared pool of email/SMS usage. However, you have to request it and approval is case-by-case. help.klaviyo.com

So I'd investigate that if you have, say, 5–15 stores and enough volume to negotiate.

Downside: it can get expensive quickly, and you're generally maintaining separate Klaviyo accounts for separate stores.

3. Brevo — best if cost is the overriding concern

Brevo is worth considering if you don't need the ecommerce-specific depth of Omnisend/Klaviyo.

Its current free plan includes 300 email sends/day, up to 100,000 contacts, and both email and SMS campaigns. Paid plans start at $9/month. help.brevo.com

I'd favor it for clients who need straightforward newsletters, promotional campaigns and SMS rather than elaborate ecommerce lifecycle automation.

What I'd do if I were running your agency

I'd standardize on Omnisend, unless your clients are already heavily invested in Klaviyo.

Build a reusable agency "master" system:

Core automations

• Welcome series
• Abandoned cart
• Browse abandonment
• Post-purchase
• Cross-sell
• Win-back
• Review request
• VIP/customer appreciation

Then create a master template library that you customize per client.

That matters more than saving another $5–10/month per account: if you can deploy a new client's email/SMS system in a couple of hours instead of 1–2 days, the agency economics become much better.

One thing I'd want to know before making the final recommendation

If you tell me roughly:

1. Number of stores: e.g. 5, 10, 25
2. Average contacts/store: e.g. 2,000
3. Shopify/WooCommerce/etc.
4. Approximate monthly email sends/store
5. Whether clients pay the software bill or you do

…I can work out which platform would actually be cheapest for your agency, including the multi-store/billing implications, rather than just comparing headline prices.

For an agency managing multiple ecommerce shops on a tight budget, I’d shortlist these three:

1. Omnisend — my pick for you

This is probably where I'd start.

Omnisend is specifically built around ecommerce and lets you manage multiple stores from one account, with separate data, automations, reporting and permissions for each store. More importantly for an agency, you can reuse templates and workflows across stores rather than rebuilding everything. support.omnisend.comwww.omnisend.com

The catch: each store has its own subscription, so don't expect one cheap account to cover unlimited clients. support.omnisend.com

Current pricing is attractive: Standard starts at $16/month, while Pro starts at $59/month and adds SMS; current SMS pricing starts at $0.007/message for high-volume US/Canada sending. support.omnisend.com

Why I'd choose it: you get the ecommerce-specific flows you actually need—welcome, abandoned cart, browse abandonment, post-purchase, winback, etc.—without paying Klaviyo-level prices.

One important 2026 change: for new subscribers after May 4, 2026, SMS requires Pro, so factor that into your per-client cost. support.omnisend.com

2. Klaviyo — best if clients can afford it

Klaviyo is still the stronger choice if you're doing sophisticated segmentation, personalization and reporting.

It's also become quite agency-friendly. One login can access multiple client accounts, and Klaviyo Portfolio gives you centralized performance, billing and user management. You can even clone campaigns, forms, segments and templates across accounts. help.klaviyo.com

For an agency specifically, bulk user management across client accounts is a big operational advantage. help.klaviyo.com

The downside is simply cost. Klaviyo bills each account based on its profiles/email and separately for mobile messaging, so having 10–20 small clients can get expensive quickly. help.klaviyo.com

There's also a potentially interesting option for larger client groups: Klaviyo offers shared billing for up to 20 accounts, subject to approval. help.klaviyo.com

I'd use Klaviyo when: the client has enough revenue that better segmentation/analytics can justify the extra software cost.

3. Brevo — best ultra-budget option

Brevo is worth considering if your clients have small lists and relatively simple requirements.

Its free plan includes 300 emails/day, up to 100,000 stored contacts, and both email and SMS campaigns. Starter starts at $9/month. help.brevo.com

The problem is that it's less purpose-built for ecommerce than Omnisend/Klaviyo. If you're managing Shopify/WooCommerce stores and want a standardized library of ecommerce automations, I'd rather have Omnisend.

What I'd do if I were your agency

I'd actually standardize on two tiers:

Small/low-revenue clients → Omnisend
Larger/high-value clients → Klaviyo

Then build a common agency playbook:

1. Welcome series
2. Abandoned cart
3. Browse abandonment
4. Post-purchase
5. Cross-sell
6. Winback
7. VIP/customer segment
8. Promotional email/SMS campaigns

Build the templates/flows once, then adapt the branding, products and offers for each store.

Omnisend is particularly compelling for this model because it explicitly supports sharing templates/workflows between stores. support.omnisend.comwww.omnisend.com

If you're talking about 5–50+ Shopify stores, I can also compare the actual monthly cost per store at 1k / 5k / 10k contacts, including SMS, and tell you which setup will be cheapest for an agency.

For an agency managing multiple ecommerce shops on a tight budget, I’d shortlist these:

1. Omnisend — my first choice

This is probably the best fit for your situation.

• Built specifically for ecommerce rather than generic email marketing.
• Supports multiple stores, with easy switching between them.
• You can create templates/workflows once and reuse them across stores. www.omnisend.com
• Email, SMS, and push are handled in the same platform.
• Pricing is generally considerably lower than Klaviyo, especially as lists grow. Omnisend currently starts around $16/month for its paid tier. www.omnisend.com
• Particularly attractive if your clients are smaller Shopify/WooCommerce brands and don't need sophisticated CDP-level analytics.

Agency advantage: you can standardize your agency's lifecycle framework—welcome, abandoned cart, browse abandonment, post-purchase, winback, etc.—then adapt the branding/content for each shop rather than rebuilding everything.

2. Klaviyo — best if your clients are bigger

I'd use Klaviyo when a client's revenue/list size justifies it.

Its big advantage is data depth: sophisticated segmentation, behavioral targeting, predictive analytics, and very deep ecommerce integrations. The downside for a budget-conscious agency is that pricing scales substantially with contacts. For example, current published pricing puts 50K contacts at roughly $720/month for email alone, before meaningful SMS usage. www.omnisend.com

So I'd avoid putting every tiny client on Klaviyo just because it's the industry standard.

3. Drip — worth considering for email-heavy clients

Drip is a solid ecommerce automation platform, but I'd put it behind Omnisend if SMS is an important part of your service. Your use case favors having email + SMS + ecommerce functionality together rather than assembling multiple tools.

What I'd do if I were running the agency

I'd actually use a two-tier stack:

The important thing is not to force every client into the same platform. Your agency can standardize the strategy, templates, flows, reporting and processes while letting the underlying ESP vary.

For your specific requirement—multiple shops + shared campaign assets + email/SMS + tight budget—Omnisend is the one I'd test first. Its multi-store functionality is unusually relevant to an agency: templates and workflows can be reused across stores, and you can switch between stores without repeatedly logging in. www.omnisend.com

If you tell me roughly how many shops you manage, average contacts per shop, and whether they're mostly Shopify/WooCommerce, I can work out which setup would likely be cheapest—including the difference between giving each client their own account vs. managing everything through an agency account.

If you’re an agency managing multiple ecommerce shops on a tight budget, I’d optimize for low cost per client + easy account separation + solid Shopify/WooCommerce integrations + email/SMS automation, rather than picking the most powerful enterprise platform.

My shortlist

1. Omnisend — my first choice

For an agency specifically focused on online shops, I'd start here. It's ecommerce-native, combines email + SMS + automation, and is generally cheaper than Klaviyo at comparable contact counts. Current comparisons show Omnisend particularly pulling ahead as lists get larger. www.omnisend.com

The big advantage for you is that you don't need to sacrifice ecommerce functionality just to keep costs down: abandoned-cart, post-purchase, segmentation, product-oriented campaigns and multichannel workflows are central to the product.

Omnisend pricing

I'd use this when: most of your clients are Shopify/WooCommerce stores and you want one standardized system your team can learn.

2. Brevo — best if the budget is really tight

Brevo is particularly interesting for an agency because its email pricing is primarily send-volume based rather than active-contact based. That can be dramatically cheaper when clients have large databases but don't send constantly. Its platform also combines email, SMS, CRM and automation. www.omnisend.com

For example, its current entry pricing starts around $9/month for 5,000 emails, while the free tier supports a very large contact database but limits daily sending. www.omnisend.com

Brevo pricing

I'd use this when: you have lots of smaller clients and want to minimize your software overhead.

3. Klaviyo — don't make it your default for every client

Klaviyo is arguably the strongest choice when a store has sophisticated segmentation, lots of behavioral data and significant revenue flowing through email/SMS. But its pricing scales with active profiles, and SMS is an additional cost. www.omnisend.com

That makes it harder to justify across 10, 20, or 50 small client accounts.

I'd reserve Klaviyo for clients where the additional revenue generated by its deeper analytics/automation clearly outweighs the extra subscription cost.

Klaviyo pricing

What I'd actually do as an agency

I'd standardize around two tiers:

Small/low-volume clients → Brevo
Cheap, straightforward, shared agency processes, email + SMS without paying a premium for ecommerce sophistication.

Serious ecommerce clients → Omnisend
More ecommerce-specific automation and better fit for stores where lifecycle marketing is a meaningful revenue channel.

Then upgrade exceptional clients to Klaviyo only when their size/complexity justifies it.

One important consideration: don't assume "one master account for all shops" is the cheapest architecture. You generally want each client's store/customer database logically isolated, while your agency has centralized access/management. Otherwise permissions, billing, unsubscribe compliance, reporting and client offboarding can become painful.

If you tell me roughly how many shops you manage (e.g. 10/30/100), average contacts per shop, and whether they're mostly Shopify, I can work out which setup is likely to be cheapest and give you an estimated monthly agency software bill.

For an agency managing multiple ecommerce shops on a tight budget, I’d shortlist these:

🥇 My pick: Omnisend

I'd start with Omnisend, particularly if most of your clients are Shopify/WooCommerce/BigCommerce stores.

The big advantage for an agency is that Omnisend was designed around multiple stores: you can switch between stores from one account, give different team members store-specific permissions, and reuse campaigns/workflows across stores. www.omnisend.comsupport.omnisend.com

Even better, their Partner Portal has templated accounts: you can build automations, campaigns and signup forms once and copy them into client stores. That's extremely useful if you're repeatedly setting up abandoned-cart, welcome, post-purchase, win-back, etc. support.omnisend.comwww.omnisend.com

The catch is important: each store still has its own subscription, so Omnisend doesn't magically consolidate all your clients into one cheap bill. www.omnisend.comsupport.omnisend.com

For new subscriptions, SMS is currently on the Pro plan, with US SMS pricing starting at $0.007/message at high volume. support.omnisend.com

💰 Brevo if minimizing software spend is priority #1

Brevo is worth serious consideration if your clients have relatively small lists or don't need sophisticated ecommerce segmentation.

Its free plan includes email and SMS campaigns, and paid plans start at $9/month. help.brevo.com

It also has an explicit agency model, letting you switch between client accounts from your agency account and manage clients centrally. www.brevo.com

I'd choose Brevo when the agency's priority is "get 10–20 small shops running campaigns cheaply" rather than maximizing ecommerce automation.

🧠 Klaviyo if your clients can afford it

Klaviyo is the one I'd use for higher-value stores where sophisticated segmentation, attribution and automation justify the cost.

It supports multiple accounts under one login, and agencies can use portfolios to oversee multiple accounts. help.klaviyo.com There is also a shared-billing program that can link up to 20 accounts and pool email/SMS usage, although approval is case-by-case. help.klaviyo.com

That's potentially very interesting for an agency—but I wouldn't make Klaviyo the default for budget clients.

What I'd actually do in your shoes

I'd use a two-tier agency stack:

Small/budget clients → Omnisend or Brevo
Larger/revenue-focused clients → Klaviyo

And standardize your agency around a reusable library of:

• Welcome series
• Abandoned cart
• Browse abandonment
• Post-purchase
• Cross-sell
• Win-back
• VIP/customer segmentation
• Promotional email/SMS templates
• Holiday campaign templates

If your shops are mostly Shopify, I'd lean Omnisend. Its multi-store + reusable-template workflow is unusually well suited to an agency model. support.omnisend.comwww.omnisend.com

If you tell me roughly how many shops you manage, average subscriber count per shop, and whether they're Shopify/WooCommerce/etc., I can work out which platform would be cheapest at your actual scale and how I'd structure the accounts.

For an agency managing multiple ecommerce stores on a tight budget, I’d shortlist these three:

1. Omnisend — best budget/value choice

This would be my first choice if the stores are primarily Shopify/WooCommerce-style ecommerce businesses.

• Built specifically around ecommerce email + SMS.
• Current Standard pricing starts at $16/month (with a temporary 30% introductory discount shown currently), while Pro starts at $59/month. support.omnisend.comwww.omnisend.com
• Pro includes unlimited email and SMS is available as a volume-priced add-on, currently starting at $0.007/SMS for high-volume U.S. sends. support.omnisend.comwww.omnisend.com
• Strong automations for abandoned cart, welcome, post-purchase, winback, etc.
• They explicitly support ecommerce agencies/partners. support.omnisend.com
• Free migration of lists, segments, flows and templates is a nice bonus when consolidating stores. support.omnisend.comwww.omnisend.com

The catch: their new pricing makes SMS Pro-only for customers subscribing from May 4, 2026 onward. support.omnisend.com

2. Klaviyo — best if you want a serious agency platform

I'd pick this if your agency expects to grow and clients are willing to pay more for sophisticated segmentation, analytics and automation.

Klaviyo is particularly interesting for your use case now because it has multi-account/portfolio functionality. A single login can access multiple client/store accounts, and portfolios provide consolidated performance, billing and account visibility. help.klaviyo.com

It also has newer organization-level administration and agency-oriented tooling. help.klaviyo.com

Big downside: cost. If you're managing a lot of small stores, separate Klaviyo accounts can become expensive relative to the revenue you're generating for each client.

3. Brevo — best ultra-low-cost/generalist option

Brevo is worth considering if price is the overriding concern.

Its free plan includes email and SMS campaigns, with 300 email sends/day, and paid plans start at $9/month. help.brevo.com

It also has an agency partner setup where you can switch between client accounts and let your colleagues access/manage those accounts. help.brevo.com

The major caveat is that Brevo's centralized sub-organization management is an Enterprise feature, so you don't get the full agency-control experience cheaply. help.brevo.com

What I'd do in your position

The important architectural point: I wouldn't put all your clients' customers into one giant shared marketing database. I'd generally keep one account/workspace per store, but give your agency team centralized access and standardized templates, flows, naming conventions and reporting.

That gives you client isolation while still allowing your team to operate efficiently.

If you're managing, say, 10–50 Shopify stores, I can also compare the actual monthly agency cost of Omnisend vs Klaviyo vs Brevo at different store/customer counts—that's probably the most useful next step for a tight-budget agency.

For an agency managing multiple ecommerce stores on a tight budget, I’d shortlist these three:

My pick: Omnisend

For your particular situation, I'd start with Omnisend.

It lets you connect multiple stores under one account and switch between them without separate logins. More importantly for an agency, you can create an email template or automation once and reuse it across stores. It supports email, SMS and push in the same platform. support.omnisend.com

The current pricing is also unusually attractive for smaller shops: Standard starts at $16/month, while Pro starts at $59/month and adds SMS; current SMS pricing starts around $0.007/message for US/Canada at the applicable volume tier. support.omnisend.com

The catch: each store still has its own subscription, so you don't get one giant shared pool of contacts/billing across all clients. support.omnisend.com

Brevo is worth considering if cost is the #1 priority

Brevo is particularly interesting for an agency because its agency program provides centralized multi-account management, so you can switch between client accounts from one place. www.brevo.com

Pricing starts at $9/month, with email + SMS available, although SMS is charged separately. help.brevo.com

I'd choose Brevo if your stores are relatively simple and you're trying to minimize software costs. I'd choose Omnisend if ecommerce-specific automations—abandoned cart, post-purchase, product recommendations, browse abandonment, etc.—are central to what you're selling clients.

Klaviyo if clients can afford it

Klaviyo is probably the strongest choice if you're managing more sophisticated ecommerce programs and want excellent segmentation, analytics and automation.

It supports multiple accounts under one login, and Klaviyo has a shared-billing program allowing up to 20 accounts (one parent + 19 children), although approval is case-by-case. help.klaviyo.com

However, I wouldn't make it the default for a tight-budget agency. Klaviyo also changed its mobile messaging pricing to per-message dollar rates in July 2026, so SMS costs need to be modeled carefully for each client. help.klaviyo.com

What I'd actually do

If you have, say, 10–30 Shopify stores, I'd structure it like this:

Agency standard → Omnisend

• One agency login
• One store/account per client
• Standardized welcome flow
• Abandoned-cart flow
• Browse abandonment
• Post-purchase flow
• Win-back flow
• Standard campaign templates
• Reusable agency-built templates/workflows
• Client-specific branding and segments

Then move only your larger/more sophisticated clients to Klaviyo if they need its deeper capabilities.

One important distinction: if by "shared ecommerce email and SMS" you mean one central platform where your agency can pool contacts/billing across all clients, rather than simply managing multiple separate store accounts from one dashboard, that's a different requirement. I can compare the economics of that setup specifically—including what it would cost for, say, 10 stores × 5,000 contacts each.

For an agency managing multiple ecommerce stores on a tight budget, I’d prioritize one platform per client/store, strong ecommerce integrations, reusable flow templates, and predictable SMS costs rather than trying to force every client into the most sophisticated platform.

My shortlist

1. Omnisend — my default recommendation

I'd probably standardize your agency around Omnisend unless a client has a reason to need something more advanced.

It's specifically ecommerce-focused and combines email, SMS, automation, segmentation and web push. The current paid plans start at $16/month for Standard, while Pro starts at $59/month; importantly, for new subscribers since May 4, 2026, SMS is on Pro with usage-based pricing starting at $0.007/SMS in the US/Canada. support.omnisend.com

That makes it particularly attractive when you're managing lots of smaller stores: you're not paying Klaviyo-level prices simply to have abandoned-cart, welcome, post-purchase and winback flows.

I'd use it for: Shopify/WooCommerce stores doing roughly $0–5M/year where your agency wants a repeatable setup.

2. Klaviyo — keep it for your bigger clients

Klaviyo is still the one I'd choose when the client has substantial customer data and you're doing sophisticated segmentation, attribution, predictive analytics, etc.

The catch for a budget-conscious agency is cost. For example, current pricing cited for 10,000 contacts is around $150/month for email and $165/month with SMS, versus Omnisend's substantially lower-cost positioning. www.omnisend.com

So I wouldn't make Klaviyo your universal agency standard unless your clients' revenue justifies it.

3. Brevo — worth considering for tiny clients

Brevo is interesting if your priority is keeping the absolute software bill down and the stores don't require extremely sophisticated ecommerce segmentation.

I'd put it behind Omnisend for a serious DTC operation, though. Omnisend's ecommerce-specific workflows make it easier to standardize an agency's implementation.

What I'd actually do as an agency

I'd create two tiers:

Agency Standard → Omnisend

• Smaller/mid-market ecommerce clients
• Email + SMS
• Welcome flow
• Abandoned cart
• Browse abandonment
• Post-purchase
• Winback
• Promotional campaigns
• Basic segmentation
• Reusable agency templates

Agency Premium → Klaviyo

• Larger stores
• Complex product/customer data
• Advanced segmentation
• Predictive analytics
• Sophisticated attribution
• Clients where an extra $100–500+/month is insignificant relative to revenue

That gives your team one inexpensive operating system for most accounts, while avoiding the mistake of putting every client on the same expensive platform.

One other important point: don't try to put all your clients into one shared sending account. Keep each brand's audiences, domains, consent records, analytics and sending reputation separated. What you want to share is your agency's templates, SOPs, flow architecture and reporting process, not the customer databases.

If you tell me roughly how many stores you manage, average contacts/store, Shopify vs WooCommerce, and approximate monthly SMS volume, I can run the numbers and recommend the cheapest setup across 10/25/50+ client stores.

For an agency managing multiple ecommerce stores on a tight budget, I’d prioritize platforms that let you centralize access, reuse campaigns/flows, and keep each client’s data separated.

My shortlist

I'd start with Omnisend. It is unusually well suited to an agency: one account can manage multiple stores, you can switch between stores, assign permissions by store, and—importantly—you can create reusable campaign/automation templates and copy them across client stores. support.omnisend.com

The catch is that each store still has its own subscription, so it isn't one cheap account that magically covers all your clients. support.omnisend.comsupport.omnisend.com

Omnisend's current pricing is attractive for smaller shops: Standard starts at $16/month, while Pro starts at $59/month and is the plan that supports SMS for new subscribers, with SMS starting at $0.007/message in the US/Canada at qualifying volume. support.omnisend.com

Where Brevo gets interesting

Brevo is worth considering if your clients have relatively modest sending volumes but large contact databases. Its free plan currently allows 100,000 stored contacts and 300 email sends/day, and includes both email and SMS campaigns. Paid plans start at $9/month. help.brevo.com

The downside for an ecommerce agency is that I would generally favor Omnisend's ecommerce-oriented workflows, store management, and reusable templates over Brevo if Shopify/ecommerce automation is the core of your service.

When I'd pay for Klaviyo

I'd use Klaviyo when a client's revenue justifies more sophisticated segmentation, predictive analytics, attribution, and lifecycle marketing. It's excellent, but if you're managing 10–20 smaller shops, putting every client on Klaviyo can become unnecessarily expensive.

What I'd do as an agency

I'd build an Omnisend agency template library:

• Welcome series
• Abandoned cart
• Browse abandonment
• Post-purchase
• Cross-sell
• Win-back
• Review request
• VIP/customer segmentation
• Promotional email + SMS templates
• Holiday/Black Friday campaigns

Then customize branding, products, offers, and segmentation for each shop. Omnisend specifically supports agency partner templates that can be copied into client stores, which could save a substantial amount of production time. support.omnisend.comsupport.omnisend.com

Bottom line:
Omnisend = my recommendation for your agency.
Brevo = investigate if minimizing software spend is the absolute priority.
Klaviyo = reserve for higher-revenue clients where advanced lifecycle marketing can pay for itself.

If you tell me roughly how many stores you manage, average contacts/store, monthly email volume, and whether they're mostly Shopify, I can work out which setup would likely be cheapest and what I'd charge clients for it.