We head already configured creating issues or adding comments to an issue by E-mail. It worked for some time, but then it stopped to work.
Analyzing the problem I've checked the configuration of the POP7IMAP-Server and the configured Mail-Handler. Everything looks fine and when I press "TEST"-Button, Test succeeds.
When I have the details shown, it shows:

To examine this, I have configurd another POP-Server and another Mail-Handler for another project. Click on "Test"-Button succeeds as well
.
So I thought, the configuration of this Mail-Handler looks fine, but it doesn't work either.