AltaMail will synchronize the app unread badge count across devices when the settings allow this. This means that when you read an email on one device, the badge count is adjusted for your other devices.

In the edit notifications screen, you should choose which accounts to view for the app badge. By default the favourites accounts are used. View
The badge sync will not happen if the 'Clear on exit' setting is on in the edit notifications screen.

In order for the sync to happen, each account used for the app badge will need to have the following settings.

1) The 'Sync incoming mail' setting needs to be turned on. This is found in the edit account screen - advanced section.
2) The email account kust be of type IMAP or Exchange. POP accounts do not support badge sync.
3) The 'Max age (days)' setting needs to be turned off. This is found in the edit account screen - settings section.
4) Notifications need to be turned on for each email account. You also need to enable quick notifications.