Originally Posted by MikeSmoke

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

tooth AT gmail.com
SMTP error from remote mail server after RCPT TO:<tooth AT gmail.com>:
host gmail-smtp-in.l.google.com [74.125.65.27]:
550-5.1.1 The email account that you tried to reach does not exist.

(I have replaced @ with AT)