Franck Martin writes:

May be a captcha? Or some more modern techniques...

Captchas aren't applicable to email requests. It will be harder than that.

We could turn off subscription by email after user creation so that users would get only one email per email at most. From Mailman's point of view:

<== subscribe email to list1 === create user for email ==> OTK to email, says "please visit URL, email operation admits abuse" <== subscribe email to list2 === recognize email, queue this request for user <== visitor arrives ==> You have (2) pending subscription requests: [x] confirm all subscriptions [x] subscribe email to list1 [x] subscribe email to list2 [submit confirmation and login to options] [just submit confirmation]

The confirmation page would recommend adding other emails to the user for security and posting convenience.

Of course a bot that knows all of a person's email addresses can do

<== subscribe email1 to list1 <== subscribe email2 to list2 <== subscribe email3 to list3

resulting in three messages in the inbox, but that's probably orders of magnitude improvement over requesting subscription of one email to all the lists on a large server.

For users who can't use/hate the web, I suppose you could allow email reply confirmation, in which case email operations would remain effective until the user explicitly turns them off.

Finally, we could keep the users with no subscriptions in the database (at the person's option), preventing the felon from waiting until the subscription requests expire then bombing the person again.

WDOT?

Steve