Fastmail IMAP and SMTP settings
Fastmail supports IMAP, SMTP, JMAP and CalDAV on its own infrastructure. App passwords are required when 2FA is enabled.
imap.fastmail.comport 993 · SSL/TLS
smtp.fastmail.comport 465 · SSL/TLS
Username
your full email addressConnect in three steps
- 1
Create an app password in Fastmail → Settings → Privacy & Security → App Passwords.
- 2
Use the full address as the username.
- 3
Prefer JMAP if you're building a new client — it's Fastmail's modern API.
What usually breaks
Fastmail requires app passwords when two-step verification is enabled (and encourages it always).
Custom domains hosted on Fastmail still use fastmail.com hosts.
Resolve it instead of hardcoding it
A custom domain on Fastmail has the same MX infrastructure as the consumer product. That is what mailintel reads.
import { mailintel } from "mailintel";
const result = await mailintel("[email protected]");
result.provider; // "fastmail"
result.connection.imap; // { host: "imap.fastmail.com", port: 993, security: "tls" }
result.connection.smtp; // { host: "smtp.fastmail.com", port: 465, security: "tls" }
result.connection.username; // "[email protected]"What is Fastmail's IMAP server?+
imap.fastmail.com on port 993 using SSL/TLS. The username is the full email address.
What is Fastmail's SMTP server?+
smtp.fastmail.com on port 465 using SSL/TLS. Most clients also accept the alternate submission port with STARTTLS.
Does Fastmail need an app password?+
Not necessarily — a regular mailbox password works, though a dedicated app password is still a good idea if the provider offers one.