Fastmail Not Syncing Across Devices
Fastmail is IMAP-based end to end, so in my experience most sync gaps come down to one specific app falling behind rather than an account-wide problem. The web app itself is very rarely the actual source.
1. Confirm it's one app, not everywhere
Check fastmail.com directly. New mail's there but missing on one device? The problem's local to that device's app, not your account.
2. Check app password status (for third-party IMAP clients)
Fastmail wants app-specific passwords for third-party mail clients — your main login won't work for IMAP/SMTP setup at all.
- Settings → Password & Security → App Passwords.
- Confirm the one your mail client is using still shows as active — a deleted or regenerated one stops working immediately, with no warning.
- Not sure? Revoke the old one, generate a fresh one, update it in your app.
3. Re-sync a lagging folder
In desktop clients like Thunderbird or Outlook, right-click the account or folder and look for a "resync" or "empty local cache and redownload" option. This fixes most local sync database corruption without needing to remove and re-add the whole account.
4. Check folder subscriptions
Because Fastmail is IMAP-based, folders need to be "subscribed" in some clients to show up at all. If an entire folder — not just new mail — is missing on one device, check that app's subscription settings.
5. Mobile app not updating
- Check background app refresh or battery optimization isn't restricting the Fastmail app.
- Manual pull-to-refresh not bringing in new mail? Log out and back in.