I see you're running the beta version. Please translate the error message to English and someone here may have suggestions. thank you.

Hello, I keep getting an error message when retrieving my mails and I can't explain it. I also don't know what it wants. I have a screenshot but can't upload it now.

The error (see picture) indicates you have too many connections to the mail server. If you have other devices, especially phones, simultaneously connecting to gmx, turn them off and see if TB responds.