Blacklist function does not work

The blacklist function is supposed to allow admins to create a blacklist of addresses so that admins don't have to repeatedly reject posts from the same email.

To reproduce:

  1. send a message to testy@lists.riseup.net from a non-member address.
  2. moderate the message and click "add to blacklist"
  3. send again from the same address, the message will appear for moderation.

This was first reported in this ticket:

https://user.riseup.net/ticket/924718

(from redmine: created on 2012-02-20, closed on 2014-06-27)