Trying to solve but something is really beyond my knowledge. As suggested in this post by @Joe:
Pick one (1) domain to use for mail, and click “Copy to Postfix”. Stop there. You’re done. Use that domain for anything that interacts with SMTP, always
I copied to Postfix but I continue to not receive e-mails. Do I have also Set as default services certificate?
Moreover, when I ask to Read mail in file or Maildir
the answer is: Failed to open Maildir/ : No such file or directory
Does it have anything to do with my issue?
Thank you all for any further assistance.