New mail shows up the moment it arrives, with three buttons.
- Mark as read — and the notification goes.
- Delete — to the Trash, as in the app.
- Reply all — type the reply right in the notification.
Tap the notification itself to open the conversation. New-mail notifications can be switched off in Settings → Preferences → Reading, with Notify me of new mail.
Fastmail tells a relay on opensolr.com that something changed in your account, and the relay wakes your phone. Fastmail encrypts that message with a key that only your phone holds, so the relay passes it on without being able to read it.
Without one, the app checks for new mail every 15 minutes and notifies you then, with the same three buttons. Only the instant part needs the relay, which belongs to an Opensolr account.