There is an outbreak of a new virus that appears to spread via email. Admins do not currently have a virus definition for this new strain. As a result they are blocking .zip file attachments until they can accurately and safely remove this threat from incoming mails.
In the meantime, you may have already received some of these messages. If you see a message with an attachement:
account_info-text.zip
mail_info.zip
err-mail_info.zip
[NOTE: there may be others]
You may also notice in the email the following:
"*** Attachment-Scanner: Status OK