If your SMTP server on Bell is failing to send mail from a web application with an obscure/misleading error like the following, just avoiding a foreign sender address (like @gmail.com) may solve.
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:
host smtp.bellnet.ca [188.8.131.52]
SMTP error from remote mail server after MAIL FROM:<firstname.lastname@example.org> SIZE=2471:
452 4.1.0 requested action aborted:
try again later #AUP504: retry timeout exceeded