It is stable when you us a thirdparty account, that means you setup gateway+smtpUser+smtpPassword.
The other mode works fine too but sometimes it hangs. let met explain there is one background thread that delivers email and sometimes the connection to an smtp server is blocking on read. Even with time out setup on the javamail stuff it happens.
If someone could reproduce that hangs it would be cool because of course it happens at random and I don't have time to reproduce that.