Mail Delivery Subsystem <mailer-daemon@googlemail.com>
13:33 (15 minutes ago)

to me 

Final-Recipient: rfc822; viking.redwolf@ubuntu.com
Action: failed
Status: 5.1.1
Remote-MTA: dns; mx.canonical.com. (91.189.95.10, the server for the domain ubuntu.com.)
Diagnostic-Code: smtp; 550 5.1.1 <viking.redwolf@ubuntu.com>: Recipient address rejected: User unknown in virtual alias table
Last-Attempt-Date: Mon, 08 May 2017 04:33:27 -0700 (PDT)