As far as I can tell there are no free forums for mailers. I used to be on one that was a part of a software program for mailers. It was very useful considering how often the USPS changes its rules. It would be nice to have access to another.
This is a good idea. We do have a Mailing forum tucked under the print finishing section: http://www.colorprintingforum.com/mailing-distribution/ It has not gotten much use to date, but I think it could be quite useful as a place to discuss the latest USPS procedures, tips, and tricks. Possibly we'll have to add some visibility and tweak the description of that forum a bit to encourage use. Thanks very much for the suggestion.