Have you considered altering the mail system? The token cost to send mail, and the ability of froobs to receive mail but not send it were poor design choices.
We don't feel that it is a poor design choice at all as it has been very effective as both a small credit drain and effectively prevented the use of spam. The new mail system has provided our paying customers a way to effectively and safely transfer items and credits. Free players who wish to remain non-subscribed can purchase the ability to use the mail systems in the account pages of the billing site which will also activate their ability to post on the forums. Maintaining control over offensive content/harassment in both the mail systems and forums with the ability to create unlimited free accounts is of course impossible...thus the purchase or limited access.