I replied to a support ticket email that I’ve replied to before successfully.
Today, my reply is rejected. I get a reply from mailer-daemon@googlemail.com that says:
Address not found.
Your message wasn’t delivered to support@u-tec.com because the address couldn’t be found, or is unable to receive mail.
The response from the remote server was:
550 5.1.1 <[support@u-tec.com]: Recipient address rejected: User unknown