smtp protocol error

["Jens Teich" <info@jensteich.de>]

I want to use gnus for my mail but get an smtp protocol error when I
try to send to another mail address than my own. The error is

| 220 h968740.serverkompetenz.net ESMTP
| EHLO JENS_SONY.jensteich.de
| 250-h968740.serverkompetenz.net
| 250-AUTH LOGIN CRAM-MD5 PLAIN
| 250-AUTH=LOGIN CRAM-MD5 PLAIN
| 250-PIPELINING
| 250 8BITMIME
| MAIL FROM: <info@jensteich.de>
| 250 ok
| RCPT TO: <jensteich@t-online.de>
| 553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)
| QUIT
| 221 h968740.serverkompetenz.net

This error doesn't make sense to me, because I am able to send emails with
Outlook Express via the same server.

Sending a mail to myself, the result is:

| X-From-Line: info@jensteich.de  Sun Nov 26 12:40:26 2006
| X-Gnus-Mail-Source: pop:info@jensteich.de@jensteich.de
| Message-ID: <upsbaiggl.fsf@totally-fudged-out-message-id>
| Return-Path: <info@jensteich.de>
| Delivered-To: info@jensteich.de
| Received: (qmail 15312 invoked by uid 60000); 26 Nov 2006 11:59:18 -0000
| Received: from 84.142.193.47 by h968740 (envelope-from 
<info@jensteich.de>, uid 60004) with qmail-scanner-1.24st SA 24
|  (spamassassin: 3.0.4.   Clear:RC:0(84.142.193.47):SA:0(0.1/9.0):.
|  Processed in 0.203409 secs); 26 Nov 2006 11:59:18 -0000
| X-Spam-Status: No, hits=0.1 required=9.0
| X-Envelope-From: info@jensteich.de
| Received: from p548ec12f.dip.t-dialin.net (HELO JENS?SONY.jensteich.de) 
(84.142.193.47)
|   by fmbook.de with SMTP; 26 Nov 2006 11:59:18 -0000
| From: info@jensteich.de
| To: info@jensteich.de
| Subject: test
| X-Qmail-Scanner-Message-ID: <116454235889615305@h968740>
| X-Spam-Checker-Version: SpamAssassin 3.0.4 (2005-06-05) on
|  h968740.serverkompetenz.net
| X-Spam-Level:
| X-Qmail-Scanner-MOVED-X-Spam-Status: No, score=0.1 required=9.0 
tests=AWL,NO_REAL_NAME autolearn=no
|  version=3.0.4
| X-Content-Length: 8
| Lines: 3
| Xref: JENS_SONY mail.misc:56
|
| test

my .emacs is

| (setq gnus-select-method '(nntp "news.t-online.de"))

| (require 'smtpmail)
| (setq smtpmail-default-smtp-server "jensteich.de")
| (setq smtpmail-smtp-server "jensteich.de")
| (setq smtpmail-auth-credentials (quote
|                 ("jensteich.de" 25 "info@jensteich.de" "secret")))
|
| (setq send-mail-function         'smtpmail-send-it) ; not for Gnus
| (setq message-send-mail-function 'smtpmail-send-it) ; for Gnus
| (setq user-full-name "Jens Teich")
| (setq smtpmail-local-domain "jensteich.de")
| (setq user-mail-address (concat "info@" smtpmail-local-domain))
|
| (setq mail-sources '((pop :server "jensteich.de"
|      :user "info@jensteich.de"
|      :password "secret")))
|
| (setenv "MAILHOST" "jensteich.de")
| (setq mail-yank-prefix "> ")
| (setq gnus-secondary-select-methods '((nnml "")))


Any clues?

Thx
-jens