ChatGPT answers, unedited

Yes. For a small agency moving websites from shared hosting to a VPS, I’d generally recommend not hosting the mailboxes on the VPS itself. Keep the VPS focused on web/app hosting and use a dedicated email provider for deliverability, spam filtering, backups, and mailbox management.

A few good fits:

My first choice: Fastmail

Fastmail Business is particularly interesting for an agency because it supports multiple domains in one account, individual mailboxes, aliases such as info@, sales@, and support@, and migration from an existing mail host. Fastmail says an account can have up to 100 domains, which is useful if you're managing mail for multiple clients. www.fastmail.com

It also means your architecture becomes:

Client domain → MX records → Fastmail → mailboxes

while:

Client domain → A/AAAA records → your VPS → website

So moving a client's website between servers doesn't require moving their email.

Fastmail's business plans are currently roughly $4–$10/user/month, depending on storage/features, with the middle tier providing 50 GB/user and custom domains. www.fastmail.help

Zoho is worth looking at too

Zoho Mail is probably the other one I'd investigate seriously for an agency. It supports custom domains, mailbox creation, distribution/group addresses, and migration from existing providers. www.zoho.com

Zoho is particularly attractive if your typical client has something like:

• 3–15 actual users
• info@, sales@, etc.
• relatively modest mailbox storage requirements
• a strong preference for keeping costs down

One important distinction

If by "scalable email hosting" you mean normal business mailboxes—people using Outlook, Apple Mail, Gmail apps, webmail, etc.—I'd look at Fastmail/Zoho/Google/Microsoft.

If you mean high-volume outbound email, cold outreach, or marketing mail, that's a different category. For example, ScaledMail sells managed mailbox infrastructure specifically for high-volume/cold-email sending, with DNS authentication and mailbox provisioning. www.scaledmail.com I wouldn't use that as the normal mailbox host for agency clients.

What I'd build for an agency

I'd actually consider making email hosting a separate service from the VPS hosting:

                 ┌── VPS / Web Hosting
Client Domain ──┤
                 └── Email Provider
                       ├── user@domain.com
                       ├── info@domain.com
                       └── support@domain.com

Then your agency can provision a new client by:

1. Add their domain to your email platform.
2. Create their users/mailboxes.
3. Set MX, SPF, DKIM and DMARC.
4. Migrate their existing mail.
5. Point their website DNS at your VPS.
6. Keep email completely independent of the VPS.

That gives you a much cleaner setup than running Postfix/Dovecot/etc. for every client yourself.

If you tell me roughly how many domains and mailboxes you're expecting (e.g. 20 clients × 5 mailboxes each), I can compare the actual monthly cost of Fastmail vs Zoho vs Google Workspace vs self-hosting mail on the VPS and recommend an agency architecture.

Yes. For a small agency moving away from shared hosting, you generally do not want to run mailboxes directly on your VPS unless you specifically want to become an email administrator. Deliverability, spam filtering, reputation management, backups, DKIM/SPF/DMARC, and abuse handling are much harder than hosting websites.

The right tool depends on whether you are:

1. Hosting your own agency mail only
2. Managing email for many client domains
3. Reselling email as part of your hosting package

Good options for an agency

If you are becoming a hosting provider for clients

Look for a platform with:

• Unlimited domains
• Unlimited aliases/forwarders
• Per-mailbox billing
• Client isolation
• White-label webmail
• API provisioning
• WHMCS/Blesta integration
• Automatic SPF/DKIM/DMARC setup
• IMAP migration tools

A platform like Atriomail is aimed specifically at agencies/hosts that want to sell email under their own brand. atriomail.com

If you are moving from cPanel shared hosting

A common architecture is:

VPS
 ├── Websites
 ├── Databases
 └── Apps

External Email Provider
 ├── clientdomain.com
 │    ├── info@
 │    ├── sales@
 │    └── staff@
 ├── anotherclient.com
 │    └── support@

Your DNS points:

• A records → your VPS
• MX records → email provider
• SPF/DKIM/DMARC → email provider

This keeps website outages separate from email outages.

For a small agency, I would usually choose:

• 5–50 internal mailboxes: Google Workspace, Microsoft 365, or Zoho Mail
• 50–500 client mailboxes: Atriomail, a white-label provider, or a managed mail platform
• Want maximum control: VPS + a mail stack like Mailcow, but only if you are comfortable operating email infrastructure

A useful question: are you trying to host your agency’s own email, or do you want to offer email hosting to your web-hosting clients as a service? The best choice changes quite a bit.

Yes. For a small agency moving away from shared hosting, you generally do not want to run mailboxes on your VPS unless you specifically want to become an email administrator. Self-hosted email brings deliverability, spam filtering, reputation, backups, DKIM/SPF/DMARC, and blacklist monitoring headaches.

The better options depend on whether you need internal agency mail only or you want to resell email to clients.

Good managed email hosting options

If you are an agency hosting client websites

I would look at a mail reseller/white-label platform rather than normal business email:

• You keep your VPS for websites/apps.
• Email lives on a dedicated mail platform.
• You can create:
  • clientname.com
  • info@clientname.com
  • support@clientname.com
  • staff mailboxes
• You manage DNS and accounts from one panel.
• You can optionally bill clients for email.

Platforms such as Atriomail specifically target agencies and resellers with white-label branding, mailbox provisioning, migration tools, and DNS automation. atriomail.com

If you only need your own agency email

A common setup:

• VPS → websites, apps, client portals
• Cloudflare → DNS
• Email provider → mailboxes

Example:

VPS
 ├── agencywebsite.com
 ├── client1website.com
 └── client2website.com

Email provider
 ├── hello@agency.com
 ├── billing@agency.com
 ├── client1.com mailboxes
 └── client2.com mailboxes

Features I would require before choosing one

For an agency, make sure it supports:

✅ Multiple domains
✅ Unlimited aliases/forwarders
✅ IMAP/SMTP
✅ Webmail
✅ SPF + DKIM + DMARC management
✅ Mailbox migration tools
✅ Catch-all addresses (optional but useful)
✅ Admin API or automation (important as you grow)
✅ Good outbound reputation

Avoid cheap shared-hosting mailboxes for client-facing businesses; they often share IP reputation with many unrelated senders.

If you are moving from cPanel shared hosting and want something like "create email accounts per client domain from one dashboard", I would specifically compare Atriomail, MXroute, Mailcow (self-hosted), and Zoho Mail. www.dreamhost.comatriomail.com

Yes. In fact, for a small agency moving websites from shared hosting to a VPS, I’d generally keep email off the VPS and use a dedicated hosted email provider. It avoids deliverability, spam reputation, backups, blacklists, and mail-server maintenance becoming your problem.

For an agency managing multiple client domains, these are particularly worth looking at:

My first choice for an agency: Migadu

Migadu is unusually well suited to the model you're describing.

It explicitly supports agencies hosting clients' email domains under one account, with multiple domains, multiple administrators, domain-level access controls, and unlimited mailboxes/addresses. Its pricing is based on account usage rather than charging separately for every mailbox. www.migadu.commigadu.com

For example, you could have:

Agency Migadu account
│
├── client-a.com
│   ├── john@
│   ├── jane@
│   ├── sales@
│   └── support@
│
├── client-b.com
│   ├── alice@
│   ├── info@
│   └── billing@
│
└── client-c.com
    ├── bob@
    └── contact@

That is much more attractive than paying for a separate email subscription for every address.

Migadu's current plans include unlimited domains and addresses, with the higher tiers increasing daily sending/receiving quotas and storage. The current Standard plan is listed at $29/month and Maxi at $99/month. www.migadu.com

Fastmail is another strong option

Fastmail Business is probably the option I'd choose if user experience and polished administration matter more than minimizing mailbox costs.

Fastmail supports custom domains, shared addresses such as support@, multiple domains, migration from existing providers, and third-party clients such as Outlook and Thunderbird. It currently supports up to 100 domains on an account. www.fastmail.com

The downside for an agency is that you're generally paying based on users/mailboxes rather than getting Migadu's "lots of mailboxes under one account" economics.

Zoho is worth considering

Zoho Mail is another good middle ground. It supports custom domains, migration from existing mail systems, aliases, centralized administration, and multiple domains. Paid organizations can currently have up to 30 domains. www.zoho.com

It's particularly interesting if your clients want more of a traditional business-email suite rather than simply IMAP/SMTP mail hosting.

What I'd do in your situation

If you're an agency and the model is:

"We host 10–100+ client websites on our VPS infrastructure, and each client may have 1–20 domain mailboxes."

I'd seriously investigate Migadu first.

The architecture becomes:

VPS
→ websites, databases, DNS management, backups, etc.

Dedicated email provider
→ MX records, mailboxes, spam filtering, SMTP/IMAP, mail reputation, backups

That separation is much safer than running Postfix/Dovecot/etc. yourself on the VPS.

One particularly nice feature for an agency is that Migadu lets you set limits at the domain/mailbox level and monitor domain health, so one client's email usage doesn't necessarily become an uncontrolled resource problem for everyone else. www.migadu.commigadu.com

If you tell me roughly how many client domains, mailboxes per domain, and total monthly email volume you're expecting, I can compare Migadu vs Fastmail vs Zoho and work out which would be cheapest at your scale.

Yes. For a small agency moving websites from shared hosting to a VPS, I’d keep email off the VPS and use a dedicated hosted email provider. It gives you much better deliverability, spam filtering, backups, and less operational headache.

My first choice: Migadu

Migadu is particularly well suited to an agency that manages multiple client domains.

• Unlimited domains and email addresses on its paid plans; pricing is based on account usage rather than charging for every mailbox. migadu.commigadu.com
• Explicitly supports agencies hosting clients' domains under one account. www.migadu.com
• Supports normal IMAP, SMTP, POP3 and webmail, so clients can use Outlook, Apple Mail, Thunderbird, etc. migadu.commigadu.com
• Has an API for managing domains and mailboxes, which is interesting if you eventually want your VPS/client-management system to provision mailboxes automatically. www.migadu.comwww.migadu.com
• Current plans include roughly $9/month for Mini, $29/month for Standard, and $99/month for Maxi, with different usage/storage limits. migadu.com

That pricing model is unusually attractive if you have, say, 30 client domains but only 80 actual users. You aren't multiplying a per-mailbox price across every address.

Other good choices

Zoho Mail — probably my second choice if you want a more conventional business-email platform. It supports custom domains, user/group addresses, and migration from an existing provider. www.zoho.com

Zoho Mail pricing

Microsoft 365 / Exchange Online — excellent if your clients live in Outlook/Office/Teams, but it's fundamentally a per-user model. Exchange Online starts at $4/user/month annually, while Business Basic is currently $4.40/user/month without Teams. www.microsoft.com

Microsoft 365 Business Email

Fastmail — very good email product and has custom domains, shared addresses, admin controls, and migration tools, but again tends to make more sense when you're managing a company's users rather than dozens of unrelated client domains. www.fastmail.com

Fastmail Business

For your particular setup

I'd architect it roughly like this:

VPS
→ websites
→ databases
→ DNS automation / client portal
→ backups

Dedicated email provider
→ client1.com
→ client2.com
→ client3.com
→ etc.

DNS
→ MX → email provider
→ SPF → email provider
→ DKIM → email provider
→ DMARC → your policy/reporting

That way, if the VPS gets rebooted, compromised, overloaded, or you migrate to another VPS, your clients' email keeps working independently.

If you're looking for something that behaves almost like “cPanel email hosting, but centralized across all my agency clients”, Migadu is the one I'd investigate first. It even has the API/admin structure to make agency-scale provisioning practical. www.migadu.comwww.migadu.com

If you tell me roughly how many domains, mailboxes, aliases/forwarders, and GB of mail you expect (e.g. 25 domains / 100 mailboxes / 300 aliases), I can compare the likely monthly cost of Migadu vs Zoho vs Microsoft 365 and tell you which model makes the most sense.

Yes. If you're moving from shared hosting to a VPS, I’d actually recommend not hosting the mailboxes on the VPS itself unless you specifically want to operate a mail server. Keeping email with a dedicated provider gives you better deliverability, backups, spam filtering, and less operational risk.

For a small agency with multiple client domains, these are worth looking at:

I'd look at Migadu first

Migadu is unusual because it is designed around the domain rather than simply charging for every mailbox. It supports multiple domains, aliases, catch-alls, standard IMAP/SMTP, and domain aliases. www.migadu.com

That makes it attractive if, for example, your agency has:

• 10 client domains
• 30–50 actual mailboxes
• addresses like info@, sales@, support@, etc.
• lots of aliases/forwarding addresses
• clients coming and going

Instead of running Postfix/Dovecot/Rspamd/etc. on your VPS, you point each domain's MX records at the email provider and let your VPS concentrate on websites/apps.

If you need shared team inboxes

I'd also investigate Shipmail. It's specifically positioning itself around agencies with multiple domains and shared addresses, including scenarios where several team members need access to things like support@clientA.com without sharing passwords. shipmail.to

That's a different use case from simply having 30 independent mailboxes.

Fastmail is another very solid option

Fastmail supports custom domains and has a straightforward migration process where you can configure the new users before switching MX records, which makes a shared-host-to-new-provider migration relatively painless. www.fastmail.help

Its business plans are priced per user, currently ranging from $4/user/month for Business Basic to $10/user/month for Professional. www.fastmail.help

For your particular architecture, I'd probably do:

Registrar/DNS → email provider → mailboxes
** ↘ VPS → websites/apps/databases**

rather than:

Registrar/DNS → VPS → self-hosted mail server

The latter is certainly possible, but email deliverability becomes an ongoing infrastructure responsibility—SPF, DKIM, DMARC, reverse DNS, IP reputation, blocklists, spam filtering, backups, abuse handling, etc.

If you tell me roughly how many domains, mailboxes, aliases, and users your agency has now (and what you expect in 1–3 years), I can compare the economics of Migadu vs Zoho vs Fastmail vs Google Workspace vs Shipmail for your specific setup.

Yes. In fact, I’d generally recommend keeping mail off the VPS and using a dedicated hosted email provider. Your VPS can run the agency’s websites/apps while a specialized mail provider handles deliverability, spam filtering, backups, and mailbox scaling.

A few good fits:

For an agency, I'd look closely at Migadu

The important distinction is that you probably don't want a provider that makes you buy a separate expensive "workspace" for every domain.

If your agency manages something like:

• agency.com
• clientone.com
• clienttwo.com
• clientthree.com

and you need:

• info@clientone.com
• support@clientone.com
• john@clientone.com
• info@clienttwo.com
• etc.

then domain/alias/mailbox architecture and pricing matter much more than raw mailbox storage.

Zoho is another very strong choice

Zoho explicitly supports adding your own domains, creating multiple users, aliases and group addresses, and migrating existing mailboxes. Its current paid plans can scale to any number of user accounts. www.zoho.com

For example, its current pricing shows Mail Lite at $1/user/month for 5 GB or $1.25/user/month for 10 GB when billed annually, with higher tiers available. www.zoho.comwww.zoho.com

It also provides a migration tool and supports SPF/DKIM/DMARC configuration, which is important when moving away from shared hosting. www.zoho.comwww.zoho.com

One architecture I'd recommend

                    ┌── VPS ── Websites
Internet ── DNS ────┤
                    ├── VPS ── Apps / databases
                    │
                    └── Email provider
                           ├── agency.com
                           ├── client1.com
                           ├── client2.com
                           └── client3.com

Your domains' A/AAAA records can point websites to the VPS, while their MX records point to the email provider.

That gives you a nice separation:

VPS: websites, applications, databases
Email provider: SMTP, IMAP, webmail, spam filtering, mailbox storage, deliverability

I would not put Postfix/Dovecot directly on the VPS unless you specifically want to become your own mail administrator. Running mail reliably is considerably more involved than running websites, particularly with IP reputation, spam, DKIM, DMARC, reverse DNS, blacklists, backups, and deliverability.

If you tell me roughly how many domains you manage, how many actual users/mailboxes per domain, and whether these are your agency's domains or client domains, I can narrow this down to the 2–3 providers whose pricing model makes the most sense for an agency.

Yes. If by “scalable” you mean multiple client domains + lots of domain-based mailboxes/aliases without having to run mail infrastructure on the VPS, there are several good options.

My shortlist

Migadu is probably the one I'd investigate first for your particular scenario. It explicitly targets web agencies and supports unlimited domains and email addresses, multi-admin access with domain-level permissions, aliases, standard SMTP/IMAP/POP3, backups, and mailbox quotas. That makes it much more aligned with an agency that might go from, say, 5 domains/30 mailboxes to 50 domains/300 mailboxes without wanting to administer a mail server. www.migadu.com

Zoho Mail is the safer mainstream choice if you want a polished business-email product. You can add domains, create individual mailboxes and groups, use aliases, and migrate existing IMAP/POP mail. www.zoho.com

Fastmail is particularly nice if these are primarily your agency's own employees rather than dozens of clients. Its business plans support custom domains, shared addresses such as support@, admin controls, and migration tooling. www.fastmail.com

One important architectural point

I wouldn't put your production email server on the new VPS just because you're moving the websites there.

A good architecture would be:

                    ┌── VPS
DNS ────────────────┤
                    │   websites / apps / databases
                    │
                    └── Email provider
                         ├── client1.com
                         │    ├── john@
                         │    ├── billing@
                         │    └── support@
                         ├── client2.com
                         └── client3.com

The VPS handles web hosting, while the email provider handles MX, spam filtering, DKIM/SPF/DMARC, mailbox storage, backups, reputation, and mail delivery.

That's especially valuable for an agency: one misconfigured VPS, compromised WordPress site, or bad outbound mail campaign shouldn't jeopardize email delivery for every client domain.

If you tell me roughly how many domains and mailboxes you expect (e.g. 20 domains / 100 mailboxes) and whether these are your agency's users or mailboxes for your clients, I can narrow this down to the 2–3 best options and compare the likely monthly cost.

Yes. If you're moving from shared hosting mail to a VPS for the websites, I would generally keep email separate from the VPS. Running your own mail server is possible, but deliverability, spam reputation, backups, DNS authentication, and IP reputation make it much more operationally expensive than it first appears.

For a small agency handling multiple client domains and domain-based mailboxes, a few options stand out:

My first choice for an agency: Shipmail

This is particularly interesting for your use case because its pricing is based on mailboxes rather than users or domains. It currently supports up to 50 custom domains per organization, with plans from 2–12 mailboxes and a Scale tier from 13–300 mailboxes. Shared inbox functionality is built in. shipmail.to

So you could have something like:

• hello@agency.com
• billing@agency.com
• support@client-a.com
• info@client-b.com
• admin@client-c.com

…and manage the domains centrally rather than maintaining separate email installations for every client.

That's a particularly good model if your agency is actually hosting/managing email for clients, rather than merely needing email for your own staff.

Migadu is worth a serious look

If your main requirement is lots of domains + lots of basic mailboxes, Migadu is compelling. It supports domain aliases and is designed around managing multiple domains from one account. www.migadu.com

I'd lean toward Migadu if you want:

"Give me a centralized place to host 30–100 relatively ordinary client mailboxes as cheaply as possible."

I'd lean toward Shipmail if you want:

"Give my agency a centralized email platform where multiple staff can work with client inboxes."

Zoho is the more conventional business choice

Zoho Mail is also very suitable. Its administration supports custom domains, user/mailbox creation, groups, aliases, SPF/DKIM configuration, and migration from existing providers. www.zoho.com

It's probably the safer choice if your clients expect something resembling a traditional business-email service rather than an agency-oriented platform.

I would not put email on the VPS by default

If you're moving:

cPanel/shared hosting → VPS

I'd structure it as:

                    ┌── VPS
                    │   ├── Websites
                    │   ├── Databases
                    │   └── Apps
                    │
Domains ────────────┤
                    │
                    └── Managed Email Provider
                        ├── client-a.com
                        ├── client-b.com
                        ├── client-c.com
                        └── agency.com

Your VPS then isn't responsible for SMTP reputation, spam filtering, mailbox storage, IMAP, DKIM signing, mail queues, etc.

You simply point each domain's MX records at the email provider and configure SPF/DKIM/DMARC.

If you tell me roughly how many client domains and mailboxes you're talking about (e.g. 20 domains / 100 mailboxes), I can compare the actual economics of Shipmail vs Migadu vs Zoho vs self-hosted Mailcow and tell you which architecture I'd use for an agency.

Yes. If the agency is moving web hosting to a VPS but doesn't want to operate its own mail server, I'd strongly recommend keeping email on a dedicated hosted-email provider. That gives you better deliverability, spam filtering, backups, and less maintenance than running Postfix/Dovecot yourself.

For an agency that may host multiple client domains, one option stands out:

1. Migadu — probably the best fit

Migadu

Migadu is specifically designed around multiple domains and large numbers of addresses rather than charging you strictly per mailbox. Its current plans allow unlimited addresses and domains, with the account's overall mail volume/storage determining the tier. The Maxi plan is currently $99/month, Standard $29/month, and Mini $9/month. www.migadu.comwww.migadu.com

For an agency, the particularly useful features are:

• Multiple client domains under one account
• Unlimited mailboxes/addresses within plan limits
• Multiple administrators with domain-level restrictions
• Per-mailbox/domain quotas
• Domain-health monitoring
• Standard SMTP/IMAP/POP3
• Aliases and catch-all addresses
• Backups
• No proprietary mail client lock-in www.migadu.comwww.migadu.com

That makes it unusually well suited to a setup like:

Agency
├── client-a.com
│   ├── john@
│   ├── jane@
│   └── info@
├── client-b.com
│   ├── sales@
│   └── support@
└── client-c.com
    ├── admin@
    └── billing@

You can keep all of those domains managed centrally while the VPS handles websites/applications only.

2. Zoho Mail — better if you want a formal reseller model

Zoho Mail Partnership

Zoho is interesting if the agency intends to sell email hosting to clients as a service. Its partnership program provides centralized management of multiple customer organizations, migration tools, partner management, and reseller capabilities. It also supports WHMCS integration. www.zoho.com

That's a stronger choice if your business model is:

"We host your website and also sell/manage your business email."

rather than simply:

"We need email for our own agency."

3. Fastmail — excellent email, less agency-oriented

Fastmail Business

Fastmail is a very good choice for a single organization. It supports custom domains, shared addresses such as support@, centralized administration, IMAP/SMTP, and migration assistance. www.fastmail.com

But if you're going to have dozens of unrelated client domains, I'd put Migadu or Zoho ahead of it.

What I would do in your situation

If the agency is moving from cPanel/shared hosting → VPS, I'd separate the infrastructure:

VPS

• Websites
• WordPress
• Databases
• APIs
• Cron jobs
• DNS if desired

Hosted email

• MX records point to provider
• Mailboxes live entirely outside the VPS
• SPF/DKIM/DMARC configured
• Webmail/IMAP/SMTP handled by provider
• Backups and spam filtering handled by provider

That way, a VPS reboot, migration, compromise, or web-server outage doesn't take down everyone's email.

My shortlist would be:

One important distinction: if by "scalable email hosting" you mean normal business mailboxes, Migadu/Zoho are appropriate. If you mean high-volume outbound/marketing/cold email, that's a different infrastructure problem; you shouldn't use ordinary employee mailboxes for that.

If you tell me roughly how many domains and mailboxes you expect (e.g. 20 domains / 150 mailboxes), I can compare the actual monthly cost and recommend the most economical architecture.

Yes. If you're moving the website/app hosting to a VPS, I’d generally keep email separate rather than running mailboxes on the VPS. That gives you better deliverability, backups, spam filtering, and much less operational headache.

For a small agency, there are a few good models:

My pick for an agency

If you mean "we're an agency and will potentially host email for multiple client domains", I'd look particularly closely at Atriomail.

It is explicitly designed for resellers and agencies, with white-label branding, automatic DNS management, API/control-panel integrations, unlimited domains/aliases/forwarders, and IMAP migration. Its advertised pricing starts around $1.39/mailbox/month, with 15 GB included. atriomail.com

That's quite different from Google Workspace/Microsoft 365, where you're essentially buying a productivity-suite account for every user.

If you're just looking for email for your agency itself, then Google Workspace is the safer mainstream choice. Business Starter currently supports custom-domain email and is $7/user/month with an annual commitment ($8.40 monthly), with 30 GB pooled storage per user. knowledge.workspace.google.com

Microsoft 365 is similarly strong if your clients/users live in Outlook/Office. Business plans support custom domains and 50 GB Exchange mailboxes. atriomail.comsupport.microsoft.com

One important distinction

If your agency needs something like:

Client A → 8 mailboxes
Client B → 3 mailboxes
Client C → 20 mailboxes
Client D → 2 mailboxes

…and you want to manage all of those from one agency account/control panel, don't automatically choose Google Workspace or Microsoft 365. Look at an email hosting/reseller platform such as Atriomail or similar.

If you tell me roughly how many client domains + total mailboxes you're expecting (e.g. 20 domains / 100 mailboxes), I can compare the current providers by cost, mailbox limits, storage, migration, white-labeling, APIs, and deliverability and tell you which architecture makes the most sense.

Yes. If you're moving websites from shared hosting to a VPS but don't want to run mail yourself, I'd strongly consider keeping email as a separate hosted service. That gives you VPS flexibility without taking on the deliverability, spam, DKIM/DMARC, backups, and reputation problems of self-hosting mail.

Good fits for a small agency

Zoho Mail is probably the first one I'd investigate for your use case. It supports custom domain mailboxes, groups, aliases, domain administration, and migration from existing IMAP/POP mail systems. help.zoho.com

For an agency, the important distinction is mailboxes vs. domains. If you have, say:

• 20 client domains
• 3–10 mailboxes per domain
• aliases such as info@, sales@, support@
• centralized administration

you want a provider whose pricing doesn't punish you simply for having many domains.

I'd architect it like this

VPS

• Nginx/Apache
• PHP/Node/etc.
• client websites
• databases
• automated backups

Hosted email provider

• alice@client1.com
• bob@client1.com
• info@client2.com
• etc.

DNS

• A/AAAA → VPS
• MX → email provider
• SPF → email provider
• DKIM → email provider
• DMARC → your chosen policy

This is much cleaner than running Postfix/Dovecot on the VPS. Your VPS can even be replaced without affecting mail.

Zoho specifically supports adding multiple domains, creating users/groups, aliases, and migrating existing mailboxes via IMAP. help.zoho.com

If you're looking for something that you can resell/manage for multiple agency clients, though, I'd narrow the choice differently. The key question is whether you want one agency-level account managing many client domains, or a separate email account/tenant for each client. If you tell me roughly how many domains and mailboxes you expect (e.g. 20 domains × 5 mailboxes), I can compare the best options and their current pricing.

Yes. In fact, for a small agency moving websites from shared hosting to a VPS, I’d generally recommend not hosting email on the VPS. Keep the VPS for websites/apps and put email with a dedicated mail provider. That avoids deliverability, spam reputation, backups, IP reputation, and mail-server maintenance becoming your problem.

For an agency that may manage multiple client domains and domain-based mailboxes, these are worth looking at:

My first choice: MXroute

If your agency might have something like:

• 10 client domains
• 30–100 total mailboxes
• info@, sales@, support@, etc.
• relatively modest storage requirements

MXroute is unusually well suited to that model. Its current plans advertise unlimited domains and unlimited accounts, with the Small plan at $59/year for 10 GB and higher tiers at $69/year for 25 GB and $79/year for 50 GB. It supports IMAP/SMTP/POP3. mxroute.com

It also has reseller plans, which could be particularly interesting if you're actually providing email hosting as part of your agency's service. The reseller offering includes a white-label control panel, customer logins, your branding, and your own pricing while MXroute operates the infrastructure. mxroute.com

Fastmail is nicer if mailbox quality matters more

Fastmail is a better choice if you're talking about a smaller number of users who want a really good email experience rather than maximizing mailbox count.

It supports custom domains, shared addresses such as support@, multiple domains, migration from an existing provider, and standard email clients such as Outlook and Thunderbird. Fastmail currently allows up to 100 domains in an account. www.fastmail.comwww.zoho.com

Zoho is the inexpensive "business email" option

Zoho is worth considering if you want something that feels more like traditional business email administration. Its admin console supports multiple domains, users, groups, aliases, migration, SPF/DKIM, and MX configuration. www.zoho.com

It also has a free tier for one domain and up to five users, although the free tier has limitations such as no IMAP/POP/ActiveSync. www.zoho.com

Shipmail is interesting specifically for agencies

This is one I'd investigate if your agency manages email for clients, rather than merely needing email for your own employees. Its agency offering is explicitly built around multiple client domains, shared/role-based inboxes, and adding/removing client domains. shipmail.to

The architecture I'd recommend

Rather than:

VPS → Postfix/Dovecot → all client mail

I'd do:

Domains/DNS
↓
Dedicated email provider
↓
user@client1.com
info@client1.com
user@client2.com
support@client2.com

and separately:

VPS
↓
Client websites / WordPress / apps / databases

Then configure each domain's MX, SPF, DKIM and DMARC records to the email provider.

That gives you the ability to move a client's website between servers without touching their email infrastructure.

If you're expecting a lot of client domains and mailboxes, I'd shortlist MXroute and Shipmail first. If it's only your agency's own 5–20 users, I'd lean Fastmail or Zoho.

If you tell me roughly how many domains + mailboxes you expect (e.g. 20 domains / 100 mailboxes) and whether you need to resell/white-label the email to clients, I can narrow this down to the best 2–3 options and compare the actual monthly/annual cost.

Yes. If you're moving the websites to your own VPS but don't want to run mail servers yourself, there are several good options. For a small agency, I’d generally keep web hosting and email hosting separate.

Best fits

The interesting one for an agency: Shipmail

If by "agency" you mean you're hosting email for multiple clients/domains, rather than just your own agency domain, I'd look particularly closely at Shipmail. It is explicitly designed around agencies with multiple domains and role/shared inboxes, and its model is based on mailboxes rather than forcing every person into a full productivity suite. shipmail.to

For example, you could potentially have:

client-a.com
  alice@client-a.com
  support@client-a.com

client-b.com
  bob@client-b.com
  hello@client-b.com

youragency.com
  you@youragency.com
  support@youragency.com

without tying email to the VPS running the websites.

If it's only your agency's email

I'd lean toward Fastmail or Zoho Mail.

Fastmail is particularly clean if you want "email hosting as infrastructure": custom domains, multiple users, shared addresses such as support@, third-party clients like Outlook/Apple Mail, and migration tooling. www.fastmail.com

Zoho is worth considering if cost per mailbox is the priority. It supports multiple accounts on a domain, groups/distribution addresses, and migration from an existing provider. It also has a small free tier for up to five users on one domain, although the free tier lacks IMAP/POP/ActiveSync. www.zoho.com

One important architectural point

I wouldn't run Postfix/Dovecot on the VPS just because you're moving away from shared hosting.

Running your own mail server means taking responsibility for:

• spam filtering
• DKIM/SPF/DMARC
• IP reputation
• blacklists
• backups
• mailbox storage
• malware scanning
• TLS
• outbound deliverability
• monitoring and abuse handling

The VPS can remain responsible for websites, databases, APIs, etc., while your MX records point to a dedicated email provider.

If you tell me roughly how many domains and mailboxes you need now (e.g. 10 domains / 40 mailboxes), whether they're all yours or client domains, and your approximate monthly budget, I can narrow this down to the 2–3 best architectures and compare the actual costs.