Since yesterday I have not been able to send any emails from Mail (although there is no problem with sending emails directly from my provider's email).
I receive the ominous message: We weren't able to send this message, so we've put it in your Drafts folder. Before you try sending it again, you can check to see if the address is correct and that no attachments are too large.
I have tried the recommended "fixes": run troubleshooter, delete Mail and reinstall
After reinstalling, re-adding the account does not request any connection information from me. This means this connection information must be cached somewhere. How can I delete this cache information?