Often, people wrongly typed the URL to retrieve the MMS. Please refer to the below comparison.
Wrong MMS page: http://mms.postfach.de
Correct MMS page: http://mms-postfach.de
*Take note on the (.) dot and the (-) hyphen.
Once you’re on the login page, please enter your mobile phone number and the password.
Quoted from Wikipedia:
In Germany, its home market, T-Mobile is the largest mobile phone operator with almost 36 million subscribers (As of January 2008), closely followed by its primary rival, Vodafone. The highly profitable GSM network in Germany is scheduled to be supplemented and ultimately replaced by UMTS, for which T-Mobile spent EUR 8.2 billion in August 2000 to acquire one of the six licenses for Germany.