Ubuntu provides all the local communities with a mailing list for their communication. The list is based on a wonderful mailing list management program called mailman. Mailman has a special feature that allows persons with more than one mailing address to post to a private list without caring about which of their email addresses is used. All is needed is the registered email to appear in the Reply-to headers of the message.

For example you are registered to a mailing list using the email foo@example.com and you also have the email bar@example.com. If you post to the mailing list using the bar@example.com normally your email will get rejected or holded for moderation (on a private list). If you have into the mail headers the Reply-to field with the address foo@example.com mailman will recognize you and will accept your email.

Recently an email from the social networking site Badoo appeared in Greek Ubuntu Users mailing list. The mail originated from noreply@badoo.com but it's Reply-to headers matched the email of a registered member. Therefore mailman forwarded the email and we all got the spam of Badoo.com

Since this feature of mailman is turned on by default and you cannot change the behavior through the web interface we had to find another way to protect our list from spam. Kostas Milonas, member of our community, created a list with all the social networking sites he could find. By using the "header_filter_rules" of mailman (Privacy Options -> Spam Filters -> Spam Filters) you can now block all social networking sites while maintaining the feature and keeping your users with multiple email addresses happy.

Download the list, ready for mailman with regular expressions and paste the contents in the 'Spam Filter Regexp' box of our mailman administrative web interface.