thank you very much for your hint on Gmail.
Unfortunately it doesn't work for me, sending a mail just results in
Gnutls seems to work, as status line of emacs says
"Opening STARTTLS connection to smtp.zmaw.de:465... done" and
nic@nic-laptop:~$ lsof | grep smtp.zmaw.de
gnutls-cl 15549 nic 4u IPv4 53799
TCP nic-laptop.local:46475->smtp.zmaw.de:ssmtp (ESTABLISHED)
But in buffer *trace of SMTP session to smtp.zmaw.de* nothing but a
"QUIT" appears (maybe afer I cancel sending through C-g).
Is STARTTLS really the same as SMTPS to port 465 on server?