Seriously, In the McAfee "options" there will be settings for E-mail. Look
through those settings for something like, "Check outgoing messages" or
"scan outgoing messages" and disable it. Alternatively, if McAfee has it,
check the setting for soemthing liek "server timeout protection" or "keep
server alive". The latter keeps the smtp server aware a message is coming
while checking the outgoing message, thus preventing timeouts.