IMAP settings · fastmail.com · fastmail.fm
Fastmail IMAP settings
Fastmail is strict about external access in a way that catches people out twice. Every program gets its own app password — the account password and the two-step password both fail — and on the Basic plan IMAP is not included at all, so no password of any kind will help.
IMAP connection
- Server
- imap.fastmail.com
- Port
- 993
- Encryption
- SSL/TLS
- Username
- full address
- Password
- app password
Sending, SMTP
- Server
- smtp.fastmail.com
- Port
- 465
- Encryption
- SSL/TLS
Checked against the service's own autoconfiguration file on 2026-09-15 — the same source Thunderbird reads when it fills the settings in for you. Source: autoconfig.fastmail.com, www.fastmail.help
What breaks here.
- The account password does not work over IMAP. Create an app password under Settings → Privacy & Security → App Passwords, one per program.
- The Basic plan has no IMAP, POP, CalDAV or CardDAV. If the plan is Basic, an external client cannot connect no matter what you enter — that is a billing question, not a settings one.
- The two-step verification password is not an app password either. Using it gives the same password error.
- The username is the full address; for a custom domain hosted at Fastmail it is that address, not the fastmail.com one.
Questions
The short answers
Where are app passwords created?
Fastmail Settings → Privacy & Security → App Passwords. Give the password a name, copy it once, and delete it from the same screen when it is no longer needed.
Does a custom domain change the host?
No. Mailboxes on your own domain hosted at Fastmail still use imap.fastmail.com on port 993 with SSL.
Why does my correct password keep failing?
Because Fastmail refuses the account password on IMAP by design. Only an app password is accepted — or the plan does not include IMAP at all.
Can I migrate away from Fastmail without losing anything?
Yes. The transfer copies messages, folders, flags and dates; the Fastmail mailbox is left exactly as it was.
Find out how big your mailbox is. It costs nothing.
Connect two servers, look at the size and decide. Or take the client and keep everything on your side.
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