HI Maxim, thanks for reply!

1) Interesting, I will look into the ngx_stream_core_module

2) I still have one question for Xclient = on - since I'm banged my head against it for days now:

You state: All information obtained by nginx is passed via the XCLIENT command.

Is this true for all credentials?? Like username and password as optained with a 'auth login' sequence:
Somehow, I can find: sasl_method=XCLIENT, sasl_username=username@mydomain.de in the postfix logfile.
However, I cannot find the password information...

Thanks again,
Cugar15