/e/ account mail sync can't be removed from the Mail app even if "Mail" sync is disabled in system settings

• /e/ version: 0.16-q-stable
• Device model(s): FP3

Summary

People who don't want to use their /e/ account in Mail can't.

The problem

Steps to reproduce

• Add you /e/ account in Settings > Account > Add account > /e/.
• Disable Mail sync in Settings > Account > username@e.email > Account sync > disable "Mail".
• Reset the Mail app : Settings > Apps & notifications > Mail > Storage & cache > Clear storage > OK.
• Open Mail. The /e/ account is still there. Long press on it and "Remove account" won't work.

What is the current behavior?

New mail synced although the user disables sync from the /e/OS Settings

What is the expected correct behavior?

It should respect our wish not to use /e/OS Mail, so sync should be toggled with /e/OS Settings mail sync toggle:

1. Like done for the other apps, when the synchronisation for /e/OS Mail is turned off in the /e/OS Account Manager's settings then the synchronization should stop (it could be set to "Never" in /e/OS Mail's Settings (Fetching mail > Folder poll frequency if needed) i.e the inbox in the app shouldn't get the new messages, but history could still be consulted.
2. If the user has turned off mail synchronization in the /e/OS Account Manager's settings and then goes to /e/OS Mail app and removes their account, then the mail account isn't added back in /e/OS Mail.
3. When the user reactivates the synchronisation in the Account settings, i.e. when they turn on synchronization for /e/OS Mail the mailbox is added back automatically.

Technical information

Relevant logs (adb logcat)

Relevant screenshots

Solutions

Workaround

Possible fixes