Fastmail Not Receiving Email? Fixes for Mail, Domains and Email Apps

When Fastmail mail stops arriving or an email app stops syncing, work through these checks in order. The first three take seconds and rule out the account-wide causes.

Quick checks

1. Fastmail's status: check fastmailstatus.com for a known problem.
2. Your subscription: in Settings › Billing & Plan, make sure nothing is overdue. Overdue accounts can have sending and receiving disabled, and other email apps can't connect.
3. Your storage: mail sent to a full mailbox bounces. Usage shows at the bottom of the folder list. Trash counts toward it, so empty it permanently, and use Settings › Folders to see which folders are largest.

Mail isn't arriving

• Spam: check the Spam folder and mark real mail Not spam. If spam protection is set to Aggressive or Custom, switch to Standard and ask the sender to resend.
• Blocked senders: mail from blocked addresses or domains goes to Trash. Unblock them under Settings › Filters & Rules › Blocked senders.
• Rules and address actions: in Filters & Rules, check that no rule moves or deletes the messages. Address actions run before your own rules — use View to see them.
• Wrong address: ask the sender to confirm the exact address they used.
• Pinned messages: lots of pinned emails can push new mail out of sight. Scroll past them, or choose Sort pinned with the rest.

Using your own domain?

• Select Recheck DNS in Settings › Domains.
• Your only MX records should be in1-smtp.messagingengine.com (priority 10) and in2-smtp.messagingengine.com (priority 20). Remove any others.
• Never set a CNAME record on the domain itself — it breaks email delivery.
• Make sure your domain registration is paid up.
• For a subdomain, select Edit on the domain to confirm Fastmail handles mail for it.

The SPF, DKIM & DMARC Checker shows a domain's MX records alongside its authentication records.

Apple Mail, Outlook or Thunderbird won't connect

• App password: other apps need an app password with Mail, Contacts & Calendars (or Mail) access. If it has the wrong access, create a new one and delete the old. See Fastmail security.
• Basic plan: doesn't support other email apps at all — use the web or the Fastmail app.
• Server settings: imap.fastmail.com port 993 and smtp.fastmail.com port 465, with your full Fastmail login as the username. Details: Fastmail server settings.
• “Unknown CA Certificate”: update your operating system, or install the ISRG Root X1 certificate in the app.
• Outlook stuck on “Synchronizing Subscribed Folders”: back up to a .pst file, then set the account up again from scratch.
• Very slow syncing: folders with tens of thousands of messages slow apps down. Move older mail into other folders or Archive.

Still stuck?

Can't log in at all? See logging in to Fastmail. Otherwise contact Fastmail support at support.fastmail.com.