Well hey Gunnar, you know I've always got something else to try. :-)

Pull up a web browser on the same machine that you are running
Postfix on, and try this URL:

https://127.0.0.1:465

The output should look something like:


220 mysite.web.de ESMTP Postfix (2.2.9) ready
221 Error: I can break rules, too. Goodbye.

And the /var/log/maillog file (or equivalent) should look something like:

May 17 08:51:17 mysite postfix/smtpd[17173]: connect from localhost[127.0.0.1]
May 17 08:51:17 mysite postfix/smtpd[17173]: setting up TLS connection from localhost[127.0.0.1]
May 17 08:51:17 mysite postfix/smtpd[17173]: TLS connection established from localhost[127.0.0.1]: TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)
May 17 08:51:17 mysite postfix/smtpd[17173]: warning: localhost[127.0.0.1] sent
non-SMTP command: GET /favicon.ico HTTP/1.1
May 17 08:51:17 mysite postfix/smtpd[17173]: disconnect from localhost[127.0.0.1]

This should test whether there's a local firewall issue for 127.0.0.1 on port 465, and
whether or not Postfix is able to set up a SSL connection. It if does work, then everything
sortof points back towards Thunderbird.

--
Greg