Reduce spam received from openplans mailing lists

Users have to wade through lots of spam daily.

Additional filtering needs to be added to reduce this spam.

This will probably end up being long term, as we will constantly need to tweak to maximize signal vs noise.

Scott and I have discussed the issues, and the next step is going to be to put a layer in front of mail drop host. This should cut down on a lot of spam itself. After, we can evaluate additional tools to cut even more spam.

Trac tickets:
http://trac.openplans.org/openplans/ticket/890