Hi to all

I'm trying to help a friend to set up Gnus. We have problems with
outgoing mail. A toggle-debug-on-error doesn't say very much:

Debugger entered--Lisp error: (error "Sending failed; SMTP protocol error")
 signal(error ("Sending failed; SMTP protocol error"))
 error("Sending failed; SMTP protocol error")
 smtpmail-send-it()
 gnus-agent-send-mail()
 message-send-mail(nil)
 message-send-via-mail(nil)
 message-send(nil)
 message-send-and-exit(nil)
* call-interactively(message-send-and-exit)

The settings in .gnus.el are correct as far as I can say:

(setq smtpmail-smtp-server "mail.gmx.net")
 (setq user-full-name "Stjepan Beles")
 (setq user-mail-address "b.stjepan@gmx.de")
 (setq message-send-mail-real-function 'smtpmail-send-it)
 (add-hook 'message-mode-hook 'turn-on-auto-fill)

 (setq smtpmail-auth-credentials
  '(("mail.gmx.net" 25 "***" "***")))

I've tested the same settings with my own GMX account on my machine,
and it works. mail.gmx.net doesn't require TLS. We both use Debian
Etch.

How can we get a more telling log? Can any external program produce
the difficulties (Emacs doesn't make use of the system's MTA, right?).
Could we have forgotten to install anything?

I'm sorry to ask such a diffuse question. But I'm not physically in
front of his machine. We communicate via Email. And he is still a
beginner with Emacs and GNU/Linux, so he cannot ask himself.

Thanks for help

Sven