Although I was using hotmail/livemail/outlook during my testing of email clients, most of the information is still relevant.

https://68kmla.org/forums/index.php?/topic/15763-stunnel-emailing-with-oe5-greenmail/

In a later post I linked to a copy of Mulberry 2.1, which claims support with Mac OS 7.1 or higher. If you get a Linux box or some Mac OS X machine setup with Stunnel, you should be able to access Google's SMTPS servers.