I know about the basic concepts of IMAP, but was hoping for TB to use
the cache while I am offline and do the deleting of the mails later,
Is there a setting to make this possible, maybe?
If you don't have a permanent Internet connection you can forget IMAP with v5.
I mentioned this on the Beta list a long time ago, nothing changed. I can only
recommend going back to v4.
It's not just deleting: You can remove flags, but suddenly they reappear. If
you use a remote outbox you can't even save messages. It's ridiculous.
Current version is 4.2.42 | 'Using TBUDL' information: