Email on every domain you own, from one account

"Does it support multiple domains" is almost always answered yes, and almost always answers the wrong thing. Google Workspace supports secondary domains. Microsoft 365 supports them. Fastmail supports them. What none of them do is stop billing per person on the second one, so the domain is free and the six addresses on it are not.

The useful question is therefore what changes on the invoice when a domain is added. Here, nothing does. The price is for the account, mailboxes are not counted, and a second domain is another set of DNS records rather than another line item.

The one thing that does move is storage. All the domains on an account draw on the same 10 GB pool, so the meter that matters is the total across everything, not a per-domain allowance. That is the number to watch, and it is on the dashboard.

Four records, published in that domain’s own DNS zone: MX so mail arrives, SPF and DKIM so what you send is accepted elsewhere, and DMARC so the first two are enforced rather than advisory. The panel shows the exact values for each domain and re-checks them on its own until they resolve.

DKIM is the gate. A domain will not take a mailbox until its DKIM record resolves — not the full set, only that one. That is deliberate and it exists for migrations: it lets you create the mailboxes and copy an archive across while MX still points at your old provider, so nothing about your live mail changes until you are ready to change it.

Adding a domain does not touch any other domain on the account. They verify separately, fail separately, and a domain whose records have not landed yet does not hold up the ones that have.

A household with a family domain and a separate one used for signups, so that a leak from a shopping site is contained to the name you were prepared to throw away. Both on one account, both real mailboxes.

A founder with the current company, two dormant projects and a domain bought for something that never happened — where the whole point is that a dormant domain should cost nothing to keep receiving on. Under per-seat pricing that mailbox is $84 a year to leave the lights on, so people let the address die instead and lose whatever was still arriving.

A studio with its own name plus the names of its own products. Note the word "own" — that is the boundary, and the next section is about it.

One account is one organisation. Twenty domains that belong to you, your household or your company is exactly what unlimited domains is for. Twenty domains belonging to twenty clients you invoice is not: each of those is its own organisation and needs its own account, which you are welcome to open and pay for on their behalf.

There is no number in that rule on purpose. A number is a target to sit just under and would be wrong for somebody at either end. If an account stops looking like one organisation’s own mail we write and ask first.