E-mail "security"

Some days ago someone tried to send a ZIP file to the Contiki mailing list. It seems that the person's mail server blocked the outgoing ZIP file and just created a message (sent to the list) saying that ZIP files cannot be sent. This is not uncommon, what I found weird though was the following part of the server generated message:

The ZIP-attachment sent to you was blocked.
Please inform the original sender to rename ZIP-files.

Die Ihnen gesandte ZIP-Datei wurde geblockt.
Bitte informieren Sie den ursprünglichen Absender. (Dateiendung umbenennen).

What is going on here? In the mail generated by the server that blocked the mail, there is a suggestion how to circumvent this block?
Security based solely on the ending of a file name along with a description how to avoid being blocked ... that's just blatantly stupid.