I just sent an e-mail to debian-l10n-german and got the following
error reply:
                           UNDELIVERABLE MAIL

Your message to the following recipients cannot be delivered:

<debian-l10n-german@lists.debian.org>:
     bendel.debian.org [2001:41b8:202:deb:216:36ff:fe40:4002]:
 >>> DATA
 <<< 550 5.7.1 No attachments allowed


Attachements have been allowed since I can remember (probably around the
turn of century) and they form a core part of the work on at least the
language lists, where we send files for review.

Disallowing attachement deprives the lists of a central functionality.

Please revert this change asap.