Hi to all

We have succeeded at last. The problem was that my fried was using
Emacs 21 which is standard in Debian Etch. This version is seemingly
unable to send smtp-authentification in plain text. But this is what
the German gmx relay-server requires. There is a patch on EmacsWiki
under the rubric SMTP_AUTH together with the information that the CVS
version already contains the patch. So, we installed the CVS
emacs-snapshot for Debian. Now it works.

This also explains, why it has always worked for me but not for him,
because I always use the CVS snapshot.

Thanks for all your suggestions. 

Greetings

Sven