We recently had similar issues with our messaging system and even though we do not use gmail as our client (we use SMTP) we solved the issue by restarting the ePDM file servers.
Our problem started when we updated Solidworks from 2013 to 2014, but did not update the ePDM client at the same time.
I would recomment restarting your servers as this tends reset settings and may prompt your messaging system to resume working.
Nick, I have done this already. It turns out that the port has been blocked by our internet provider or by Google I have yet to determine who. They block the port to prevent spam from being sent.
Thanks for the input though.
Turns out I had disabled the SA user in the database which is tied to the EPDM message system. Reset the password, restarted the database and the message system took off.
Lessons learned............Stay out of the #%$^$&$*(#$@# database if you don't know what your doing.
Why must I always learn the hard way.