Fastmail Aliases vs Masked Email: Which to Use for What

Fastmail aliases vs Masked Email is a question about lifespan, not features. Both are extra addresses that deliver into the same Fastmail account, both can send mail, and both can sit on your own custom domain. The difference is what you intend to do with the address in a year.

An alias is an address you picked, like [email protected] or [email protected], that you print on business cards and give to clients. A Masked Email is an address Fastmail generates for you, one per website, so that when a shop sells or leaks it you switch that single address off and nothing else is affected.

This guide gives the decision rule for each common use: client-facing mail, newsletters, retail signups and role addresses. It also covers plus addressing, the limits Fastmail publishes, and what each choice does to deliverability. Every Fastmail detail below was checked against Fastmail's own help centre in September 2026.

What is the short verdict?#

Use an alias for any address a human being is supposed to remember or reuse: your public contact address, client work, role addresses such as support@ or billing@, and the address you use for account recovery on things that matter. Aliases are chosen, stable and meant to live for years.

Use Masked Email for any address a company collects in a form: shops, trials, loyalty programmes, newsletters you are not sure about, forums, and one-off downloads. Masked addresses are random, labelled with a description so you know who each one was for, and cheap to throw away.

Use plus addressing (you+shop@yourdomain) only when you want quick sorting and do not care about privacy. It sorts well, but the part before the plus is your real address, so anyone who strips the tag can still reach you.

How do aliases and Masked Email compare at a glance?#

The table below sets the two side by side, with plus addressing added because it is the option most people already use without knowing it. Limits and behaviour are taken from Fastmail's help pages as of September 2026; Fastmail can change them, so confirm on its help centre before you rely on a number.

Where do aliases win?#

Aliases win wherever continuity matters. Fastmail describes an alias as an address that sends and receives mail through Fastmail, and you create one under Settings, then My email addresses, then Add address. Fastmail notes that a new alias can take up to 15 minutes to start working, so create it before you hand it out.

Every alias needs a target. By default that is your own Fastmail login, but Fastmail lets you point an alias at another Fastmail user or an external address, and at several targets at once. That multi-target delivery is what makes aliases the right tool for role addresses.

• Client-facing addresses. A chosen address on your own domain reads as a business; a random masked string in a proposal reads as a mistake. Clients also save your address to their contacts and search for it later, which only works if it never changes.
• Role addresses. support@, billing@ or hello@ can target several people in the account, so the role outlives any one person. Fastmail's business plans describe these as shared addresses like [email protected].
• Account recovery. Your bank, domain registrar and Apple or Google account should point at an address you will still control in ten years. That is an alias on a domain you own, not a disposable address.
• Sending with a proper identity. When you compose from an alias you can set the display name and signature per address, and set a reply-to and auto-Bcc in advanced settings. That keeps each hat you wear consistent.

How do you set up a Fastmail role address?#

A role address is just an alias with more than one target. The setup below follows Fastmail's current help article on aliases; menu names can shift, so check the article if a label has moved.

1. 1

   Add your domain first

   Role addresses belong on a domain you own. Custom domains are not available on Fastmail's Basic plan, so this needs one of the plans that includes them.

2. 2

   Create the alias

   Go to Settings, then My email addresses, click Add address and choose Create an alias. Enter the name, for example support, and pick your domain from the dropdown.

3. 3

   Set the targets

   Edit the alias and add each person who should receive it: other users in your Fastmail account or external addresses. Fastmail allows an alias to target multiple addresses at the same time.

4. 4

   Set how replies look

   Give the alias its own display name and signature, such as Acme Support, so replies read as coming from the team rather than one person.

5. 5

   File it automatically

   Use the alias's address action to move its mail into a folder or label, or write a rule. Either keeps role mail out of personal mail.

Where does Masked Email win?#

Masked Email wins wherever the other party is a database rather than a person. Fastmail generates a unique address when you click New Masked Email address under Settings, then Masked Email, and asks for a short description of the service it is for. That description is shown on messages arriving at the address, so a leak identifies itself.

Each masked address has three states, as Fastmail defines them. Active means it receives mail. Blocked means messages to it go to your Trash. Deleted means messages to it bounce, and Fastmail says deleted masked addresses can be restored at any time.

• Retail and trials. One address per shop means a breach or a sold list costs you exactly one address. Block it and the rest of your inbox is untouched.
• Newsletters you are testing. If a newsletter ignores its unsubscribe link, blocking the masked address ends it without arguing.
• Forums, downloads and gated content. These sites often want an address only to send one link. A masked address satisfies the form without joining your real identity to the account.
• Password-manager signups. Fastmail connects to 1Password, and supports Bitwarden and the Fastmask iOS app, so a new masked address can be created at the moment you fill in a signup form.

What does each choice mean for deliverability?#

Deliverability runs in two directions here: mail you send from these addresses, and how the senders writing to you react when you shut an address off.

When you send from an alias on your own domain, the recipient's server judges your domain. Follow Fastmail's DNS instructions for your custom domain so its SPF, DKIM and DMARC records are in place before you send client mail from it. A chosen address on an authenticated domain is also what a client's filters are most used to seeing from a supplier.

Sending from a masked address works, and Fastmail defaults replies to the masked address so you do not leak your real one by accident. It is best kept for replying to the service that address was made for. A random string in a cold first message to a person looks like the kind of address spam filters and humans are wary of.

Where does plus addressing fit?#

Fastmail sends any mail for alias+anything@yourdomain to the underlying alias, and if the tag matches a folder name the message is filed there without a rule. It works on any alias with no setup, which makes it a quick way to sort newsletters.

Fastmail also warns that some websites wrongly reject addresses containing a plus. Its answer is subdomain addressing, [email protected], which files the same way. It only supports one level of subdomain, and the alias itself cannot contain a dot or underscore.

Neither form hides anything. The real address is sitting right there before the plus or inside the subdomain, and list sellers know how to strip tags. Treat plus and subdomain addressing as sorting tools, and Masked Email as the privacy tool.

How many aliases does Fastmail allow, and what is included where?#

Fastmail's help centre states that accounts can have up to 600 aliases, plus 15 for every user in the account, and that legacy plans have different limits. For Masked Email it says there is a limit on the total number of addresses and on how many can be created in a period, to prevent abuse, but it does not publish the numbers. If you hit the creation limit, Fastmail suggests trying again after 24 hours.

On packaging, Fastmail's pricing page (checked September 2026) lists aliases on every current plan, and Masked Email and custom domains on every plan except Basic. Catch-all addresses need a custom domain, so they are also unavailable on Basic. We do not quote Fastmail's prices here because they change; check the plan table on fastmail.com before you choose.

Who is each one genuinely for?#

Most people need both, split by the one question above: is this address for people or for services?

• Freelancers and consultants: one alias per business or client-facing role on your own domain, and Masked Email for every tool trial and vendor signup. The alias is your reputation; the masked addresses are your shield.
• Small teams: aliases for every role address with multiple targets, and a separate Fastmail user only for someone who needs their own login, mailbox and storage. Fastmail's own guidance draws that line between aliases and users.
• Privacy-first individuals: Masked Email for almost everything, one alias for account recovery and people you know, and plus addressing never used for privacy.
• Anyone moving off another provider: keep your old public address as an alias target during the move, and switch retail accounts to masked addresses one by one as they email you, rather than all at once.

Is there a third option for the mail that still gets through?#

Aliases and Masked Email control which address a sender can reach. They do not decide what happens to the mail that legitimately arrives at those addresses, and on a busy account that is where the time goes: client threads, role-inbox requests and the newsletters you actually want, all landing in one place.

We build AI Emaily, so weigh this accordingly. It is not an alias or masking service: it cannot create aliases or Masked Email addresses, and you keep managing those in Fastmail, which does that job well. What it does is sit on top of your Fastmail account over IMAP and triage what arrives, with rules and a cold-email filter, drafts you approve before anything is sent, and an audit trail with undo. If that is the part you are missing, the [homepage](/) shows how it works and [pricing](/pricing) lists the plans, which start with a 7-day free trial.