Setting up your domain: no NS or MX

In rare cases, Fastmail isn't hosting the nameservers or MX records for a domain, but mail is still being redirected to Fastmail to host.

This option can be good if you're using a third party filtering service to process mail before it is sent to us.

On this help page, we'll provide the values you will need to set up your DNS with your domain registrar to make sure mail is delivered correctly. We won't be able to identify any setup errors, as the domain management is held elsewhere.

  1. Add your domain
  2. Apply DKIM and SPF records
  3. Add email addresses at your domain

Optional setup

1. Add your domain

  1. Go to the Settings → Domains screen.

  2. Click Add or buy domain, then select Use a domain you already own. Type your domain into the text box. We will verify that your domain is registered.

  3. Follow the prompts to add your email addresses to Fastmail. We will ask you whether or not you have a website. Choose either Yes or No.

  4. We will then offer instructions for changing either your nameserver or MX records (depending on your answer to the website question). Since you won't be changing these records, scroll to the bottom and click Close and check it later.

Fastmail will report the domain as Inactive. Since your domain isn't hosted with Fastmail and the DNS records do not point to Fastmail, this warning will remain.

Please note: The domain setup wizard can only set up additional addresses 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. Apply DKIM and SPF records

You will need to set the DKIM and SPF records with your domain server to ensure your mail is properly signed.

  1. Go to the Settings → Domains screen and click Edit next to your domain.
  2. On the following page, click Get instructions.
  3. Follow the instructions onscreen for adding DKIM and SPF to your domain registrar's DNS control panel.

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 → My email addresses screen. You may also choose to add a catch-all address 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.

You can customize other settings, such as your signature and default address, on the Settings → Signatures & Compose screen.

Optional domain setup

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 that address up, 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 addresses 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.

subdomain set up

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

  1. Subdomain addresses are handled like regular Fastmail domains, following plus addressing rules. (Recommended for ultimate flexibility)
  2. The subdomain portion is ignored.
  3. 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 team addresses 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.
  • Use 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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