Working Sendmail.mc for GMX.NET ?

[peter_(_dot_)_voigt1_(_at_)_gmx_(_dot_)_net]

This is the question of a newbie:

Is anyone able to post a working sendmail.mc, in order to use GMX.net
as a mail-relay?.

The aim is, to configure a secure openbsd 3.6 station for reading and
writing/posting emails. 

Hardware: i386 Desktop-PC
Internet-acces: pppoe via (german) t-dsl

The openbsd-proto.mc allows email-reading via fetchmail/mutt, but not sending
emails.

Googling did not help. There are some webpages about
masquerading, but nothing works for me.

Is anyone able to post a working sendmail.mc, in order to use GMX.net as
a mail relay (paid account there)?

Thanks for any help.

Yours
Peter Voigt