I am having an issue with the same thing described, but I don't understand the solution.  It seems that since I have to specify a user, password and server it won't use the user email information instead.  So, if I have to plug in the stuff manually to the Send Email Action, there is no option to check-mark SSL, which I believe why it is failing.
We also use gmail with our own domain.  I set up our user emails as username@ourdomain.com, password, imap.googlemail.com and check marking SSL.  That works, but Send Email Action does not.  Please assist in the missing information.