Limiting Subscription Requests

Mailman allows for anonymous people to subscribe to a mailing list. This can be done by the web page interface https://engineering.purdue.edu/ECN/mailman/listinfo/[LISTNAME] by filling out the web form and clicking "subscribe". However, spammers have performed mass subscriptions by using a robot to fill out the form. To limit the amount of mass subscriptions, use the following formula to adjust the Mailman mailing list settings.

Subscribe policy

The setting under Privacy options/subscribe_policy can be three values:

• Confirm
• Require approval
• Confirm and approve

The best setting is Confirm and approve. This setting would require the spambot to respond to a confirmation e-mail each time they attempt to subscribe to the mailing list, perhaps slowing them down.

Ban list

Setting a ban list will eliminate attempts to subscribe. The setting under Privacy options/ban_list can specify a regular expression that must be matched before someone can subscribe to a Mailman mailing list. Since regular expressions are sometimes difficult to read, be sure to cut and paste the line to avoid typos.

Some example values to enter into ban_list:

Only allow Purdue University e-mail addresses:

^.+@(?!(?:.+\.)?purdue\.edu$)

Ban anyone from example.com:

^example\.com

Ban everyone (only the list administrator can subscribe a member):

^.