Migadu vs Fastmail for Multiple Domains: Per-Mailbox or Flat Rate?

Choosing between Migadu vs Fastmail for multiple domains is not really a feature comparison. Both host custom-domain email competently, both speak IMAP and SMTP, both run more than one domain on one bill. The decision is made somewhere else: in how each one counts what you use.

Migadu charges a flat price per account and meters daily message volume. Fastmail charges per user on its business plans and publishes a hard ceiling on domains. Those two models give opposite answers depending on the shape of your setup — many quiet addresses, or a few busy people.

What follows compares billing structure, documented limits, client access, deliverability posture and support, from each vendor's own pages. Prices are deliberately not quoted; they move, and a stale figure is worse than none.

The verdict up front#

If you run many domains with many low-traffic mailboxes — an agency holding client domains, a family with several surnames, a founder with a portfolio of side projects — Migadu is the better structural fit. It states plainly that an account may have unlimited mailboxes and addresses, and it does not charge for any of them.

If you run fewer domains for a team of people who each send and receive a lot, Fastmail is the better fit. Per-user billing is expensive when users are cheap to serve, but it buys predictable per-user sending headroom, per-user storage, real multi-user admin tooling, and a vendor that publishes far more operational detail.

The deciding dimension is the ratio of mailboxes to message volume. Many mailboxes, low volume each, favours Migadu. Few mailboxes, high volume each, favours Fastmail. Everything else here follows from that.

At-a-glance comparison#

Both columns describe what the vendor documents, not what we measured. Where a vendor does not publish something, the cell says so rather than guessing.

Where Migadu wins: mailbox count stops being a cost#

Migadu's pricing page states the model in one line: "The plan prices are flat, per Migadu account. An account may have unlimited mailboxes and addresses." It follows that with a sentence aimed squarely at everyone who has ever priced a competitor per seat — "Forget now the idea of paying per mailbox."

That changes what you can do without thinking about it. Every project gets a real mailbox instead of a forwarding alias. Every client domain gets info@, billing@ and support@ as separate boxes. Role addresses stop being a budget line.

The domain side is equally unusual. Migadu publishes no numeric domain cap. The only restriction it documents is a soft one on the entry tier: "There is no enforced restriction of domains number on the Micro plan. However, if you do have a significant number of domains, we will raise eyebrows and may ask you to upgrade plan." Honest, but not a number you can plan against.

Storage is soft too, and Migadu is direct about it: "There are no hard storage quotas. Mails will never bounce back because of full storage regardless of your plan." The per-plan figures are guidance rather than a wall.

• Unlimited mailboxes and addresses per account, stated on the pricing page
• No published domain cap; a soft eyebrow-raise rule on the entry tier only
• Storage limits described as soft, with no bounce-on-full behaviour
• Tiers separated by daily message volume, not by seats; upgrades and downgrades prorated

The catch: Migadu meters the thing you cannot see#

Flat pricing has to be paid for somewhere, and Migadu pays for it with message quotas. Usage is counted across "all active domains and mailboxes on the account, which get counted together towards the plan quotas" — one pool, every domain, every mailbox.

Enforcement is documented in two halves that behave differently. Inbound: "When reaching incoming messages limits, we will warn you and allow for some tolerance of up to 25% over the plan limit", and "If even the higher tolerance level gets reached, we will start deferring messages until either the following day or the plan is upgraded." Deferred, not bounced.

Outbound carries the same 25% tolerance but a harder outcome: "After the tolerance we will start rejecting outgoing messages." A batch of invoices or a busy support day can stop your sending for the rest of the day across every domain, because the pool is shared.

Understand this before moving an agency onto Migadu. The unlimited part is the address space. The metered part is the traffic, it is pooled, and one noisy client domain consumes headroom belonging to all the quiet ones.

Where Fastmail wins: documented limits and real admin tooling#

Fastmail's advantage is not that its numbers are bigger. It is that they exist, in writing, on a page you can cite back to the vendor. Its account limits article publishes the domain cap as "100, plus 1 for every user in the account" — a real ceiling, and one most agencies will never touch.

The same page publishes daily sending limits per user, tiered by plan: 4,000 messages and 1 GB on Basic, 8,000 messages and 2 GB on Standard and Individual, 16,000 messages and 4 GB on Professional. Trial accounts are capped separately at 120 messages per day. Note the unit — those limits are per user, so adding a seat adds headroom rather than consuming a shared pool.

Multi-user accounts are a first-class feature. Fastmail documents that "Multi-user accounts have one or more account administrators who take care of bill payments, managing users, and setting up any domains or websites in use by the account", with admin control over password resets, user removal, per-user quotas and aliases. Users can sit on different plans in one account — "All users in the account can be on any plan" — on a single payment.

One rule catches people out on the cheapest tier: custom domains are gated. Fastmail states that "In order to use custom domains with Fastmail, at least one admin of the account must be on a non-Basic subscription plan", and its pricing comparison marks custom domains as not supported on Basic. You can put most of a team on Basic, but not all of it.

• A published domain cap — 100, plus one per user — instead of an unpublished soft rule
• Per-user sending limits that grow as you add seats, rather than a shared account pool
• Named administrators, per-user quotas, shared mail folders, contacts and calendars
• Mixed plans within one account, on a single bill, and a documented 30-day free trial

Pricing model, described honestly#

We do not publish competitor prices — hosting prices move, and a wrong figure costs a reader real money. What is stable enough to compare is the shape of each model, and the shapes are genuinely different.

Migadu sells four flat tiers — Micro, Mini, Standard and Maxi — and the only thing that changes between them is capacity: daily incoming messages, daily outgoing messages, and a soft storage allocation. Mailbox and domain count never enter the calculation. You size by traffic and stop thinking about it. Migadu also documents that you can upgrade or downgrade any time and it will "automatically prorate the unused portion to your account balance."

Fastmail sells personal plans as flat rates for a fixed number of people — Individual for one, Duo for two, Family for up to six — and business plans as Basic, Standard and Professional at a per-user monthly rate. You size by headcount, and by the storage and sending each person needs.

Run the arithmetic on your own numbers first: real mailbox count, real domain count, and a fair estimate of messages sent and received per day across all of them. One model will be clearly cheaper, and which one flips at a surprisingly low mailbox count.

Deliverability and support: what each actually publishes#

Deliverability is where multi-domain setups quietly fail, and it is where both vendors publish less than you would like. Neither documents a dedicated outbound IP for standard plans, so on both you send from shared infrastructure and inherit its reputation. That is normal for hosted email, not a criticism of either.

What Migadu does publish is a strict acceptable-use position, worth reading before you migrate a list. Its terms require that you not send "spam (junk) mail, or mailing list emails that contain persons that have not specifically agreed to be included on that list", and state that an account generating spam "will be immediately blocked", with blocked domains added to permanent blacklists. With the pooled outbound quota, the message is clear: Migadu is built for correspondence, not campaigns.

Fastmail's position is expressed in numbers instead — per-user daily message and volume caps, plus "a smaller daily, hourly, and 10-minute limit on the number of distinct recipient addresses you can send to." Same conclusion, different mechanism: a marketing or transactional stream belongs at a dedicated sending provider on its own subdomain, whichever host you pick.

Support expectations differ more than the marketing suggests. Migadu documents one route — "If you already have an account with us, please sign in and submit a support ticket", otherwise email — with no phone line, no live chat, and no published response time or hours. Fastmail runs a much larger help centre plus ticketing, and also does not document phone support. If a client will escalate an outage to you by phone at 9pm, neither vendor gives you someone to call. Price that into what you promise.

Client access and day-to-day administration#

For an agency the real question is not who owns the mailbox but who can get into it, and what happens when the relationship ends. On Migadu everything lives under one account — the source of the pricing advantage and its main operational drawback. It suits administering mail on a client's behalf. It is awkward when a client wants their own admin control, or when you exit: you are moving mailboxes out of a shared account rather than transferring an account.

On Fastmail the multi-user account is the unit, and domain management is restricted — "only account administrators can manage custom domains on an account." Better when the client is a company with its own staff; worse when you hold forty domains for forty unrelated clients, because each mailbox is a seat on the bill.

Both support the addressing patterns that make many-domain life bearable. Migadu documents catch-all handling, domain aliases, plus addressing, subdomain addressing and wildcard sending permission. Fastmail documents a catch-all (wildcard) alias and an alias ceiling that, like the domain ceiling, scales with the number of users.

Who each is genuinely for#

Pick the model that matches the shape of your setup rather than the one with the better landing page. Three profiles cover most of the people asking this question.

A third option, honestly — and what it is not#

We build AI Emaily, so take this section with the appropriate scepticism, and note what it does not claim. AI Emaily is not an email host. We do not sell mailboxes, we do not host your domain's MX records, and we cannot answer the question this post is about. Whichever of Migadu or Fastmail you pick, you still need one of them.

What we do is sit on top. AI Emaily is an AI email client that connects to Gmail, Outlook and any standard IMAP mailbox — both hosts here included — and pulls every account into one inbox. If you hold twelve client domains, the pain after billing is logging into twelve places, and a client-side layer is the part of the stack that fixes that.

The agent triages, drafts and closes loops across all of those accounts at once. Copilot mode means nothing is sent without your approval, every action is reversible, and every action is written to an audit trail — which matters when the mail is not yours. Voice comes from a Personal Context brain you set yourself plus per-client profiles you define. We do not train on your mail.

The honest limits: we inherit your host's deliverability, quotas and uptime rather than replacing them, so nothing here fixes a pooled Migadu outbound limit or a Fastmail recipient cap. There is no permanent free tier — it is a 7-day free trial on Pro or Autopilot, card required, $0 if you cancel before day seven. If what you need is cheaper mailbox hosting, the answer is above this section, not in it.