IMAP connection reuse

[ChristophWurst]

Is your feature request related to a problem? Please describe.

Afer #6174 Mail will close IMAP connection explicitly. Therefore two sections of code within the same process that acquire the same connection will now login and log out twice.

Describe the solution you'd like

Investigate if we have atomic operations in which we could keep the connection open instead of closing it in between. Yet we have to choose wisely as a stale open connection is also not what we want. Sometimes closing and reopening can be the faster and more reliable solution still.

Describe alternatives you've considered

N/a

Additional context

No response

[ChristophWurst]

Tackled via #6307.