Okay,I made more fixes today in version 1.01:

https://code.google.com/p/simplemail-mos/
http://amigapurist.scenespace.net/simplemail-mos/simplemail-mos-1.01.lha

With this version common root CAs are supported (Google Mail etc.).
Also self-signed certs can be validated permanently now.

So SSL can be used quite flawlessly now.