- Only when changes: only post a notification when something on the server changes. If this is off, you'll get a notification after every time the app checks mail.
- Sound only once: when on, and the app posts a notification with sound, and this account's notification already exists in the status bar, then the sound will not be played again. When off, there will be a sound every time.
Now, recent development builds (posted on this forum) have a new setting to only notify about "truly new" unread messages. This is in the same settings section.
- Manage per-account notifications: when off, the app will clear notifications for all accounts when you launch the app's UI. When on, it will clear each account's notification when you open that particular account's message list (folder).
This is useful if you want to catch up on just some accounts, leaving others for later.