Domain set up: MX only

  • This option is good for users who have a website at their domain, but who would like to use Fastmail to handle their mail.
  • Final set up must be done on the control panel supplied by your domain registrar. We provide you with the values you'll need to add to your DNS records.
  • We can detect some MX-related set up issues, and we'll notify you if we see any.

There are just three simple steps:

  1. Add your domain
  2. Domain registration set up.
  3. Add email addresses at your domain

Double checking the DNS changes

Optional set up

We have handy guides for setting up your domain's MX records with a few common domain registrars:

1. Add your domain

We have a setup guide to help you get your domain working as quickly and easily as possible.

Go to the Settings → Domains screen. Then, add your domain(s) (e.g.

Clicking the Add Domain button brings up the domain wizard. Type your domain into the box. We will detect whether your domain has been registered or not. It's important that the domain has already been registered by you at a domain registrar; otherwise you won't be able to make the necessary changes.

Follow the on-screen prompts to continue adding your email addresses and setting up your domain. At the end, we will generate the instructions that match your situation. The general instructions for editing your MX records are below.

Please note: The domain setup wizard can only set up aliases on legacy plans. If you are on a legacy plan, you will need to add users manually in order to create additional user accounts at your custom domain.

2. Domain registration set up

Note: Updating your DNS is a big change: we recommend updating it at a time you don't expect much mail.

Set your MX records to:

  • (first, priority = 10)
  • (second, priority = 20)

If your DNS provider asks for a host name, this can be entered as @.

These should be the only two MX records listed for your domain. If you also want email for subdomains to come to us, you need to set the MX records for * to the above values as well.

Some DNS providers require that you put a . on the end of the MX server names (e.g. rather than Try the version without a . first, and if the DNS provider adds anything, try adding the ..

In addition to MX records, we strongly recommend you add SPF and DKIM entries to help make sure messages are sent from your domain without issue. These are the values you need (make sure you replace {} with your actual domain!):

Type Selector Value
TXT (leave blank) v=spf1 ?all
CNAME fm1._domainkey fm1.{}
CNAME fm2._domainkey fm2.{}
CNAME fm3._domainkey fm3.{}

If your DNS provider requires a host name for the TXT record, this can be entered as @.

If you use Cloudflare, you should see an orange cloud icon when editing your CNAME entries. Cloudflare supports CNAME flattening, however we do not. Click on these orange clouds to direct traffic away from Cloudflare and turn off CNAME flattening.

Once we detect that your MX records are set up correctly, go to Settings → Domains, click Edit on your domain and we'll show you if everything is set up correctly.


See our DNS page for more information.

3. Add email addresses at your domain

Email addresses for your domain are added during the domain setup process. If you need to add additional email addresses at a later date, these can be added in the Settings → Users & Aliases screen. You may also choose to add a catchall alias if one was not already set up with the domain, so that any mail addressed to your domain comes to you, no matter what address is used.

Creating an alias also creates a matching Sending Identity. This lets you send mail from your account using the email address matching that alias. You can customize other settings too, such as your signature.

If you'd like to set up your account to send using one of your custom domain addresses by default:

You can also choose an Identity to use as the default for sending mail within a given folder.

Double checking the DNS changes

How long until it's working?

Depending on the TTL values for your previous DNS settings (if any), it may take up to a day for the changes to propagate across the internet. Normally it's a lot faster: just a matter of minutes. Once your domain is set up correctly and active on Fastmail, messages sent to the addresses you added on the aliases screen should now arrive in your Inbox.

How do I know it's right?

Your Settings → Domains screen shows a green tick when it has detected that your DNS entries are complete and correct. Any lingering issues are marked with a red exclamation point and a recommendation on how to resolve this issue.


There are many online tools to check the set up (such as MX Toolbox).

Optional domain set up

System email addresses

The email standard requires that the email address be a valid email address. Because of this, even if you don't set up an alias for that address, we will deliver any email sent to that address to the owner of the domain.

It's also best practice to support By default, if you don't set up your own alias for, we'll automatically direct all email sent to to our abuse handling system.

Subdomain addressing and mail routing

On the Settings → Domains screen, you can control subdomain addressing and mail routing.


The Mail: Subdomain section lets you control how Fastmail handles subdomain addressing for your domain. There are three options:

  • Subdomain addresses are handled like regular Fastmail domains, following plus addressing rules. (Recommended for ultimate flexibility)
  • The subdomain portion is ignored.
  • Mail to subdomains is disabled for your domain. This can mean two things:
    1. If the DNS for a subdomain points to us, then sending to that subdomain will be rejected and bounced.
    2. If the DNS for a subdomain points to other servers, then sending to that subdomain will direct email to the appropriate servers.

The Mail: Routing section lets you choose how mail to this domain is handled. Use:

  • Internal routing when Fastmail is handling all of your mail activities. This provides proper loop detection preventing inadvertent mail loops (via aliases or forwarding) that could cause spam or over-quota usage. While in this state, the DNS records for the domain are only checked every day.
  • External routing when some or all of your email activities are hosted elsewhere; whether this is the mail itself or things like mailing lists. No loop detection is possible. While in this state, the DNS records for the domain are checked every hour to see if they have changed.
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