Here's a question: does anyone know of, or is there any way to create, a script that would require administrative approval of an email sent to more than X number of addresses? For example, if someone sends an email to 40 cc: or bcc: addresses, is it possible to create a script that would hold that message until an administrator approves it for release?
I've got one or two legitimate users who occasionally send out newsletters to their mailing lists, but the rest of the time any emails in the queue to any significant number of people are spam. Although I keep the server locked down fairly well and manually approve all accounts, occasionally a spammer slips in somewhere...usually a danged php script exploit. Something like this would help mitigate the damage.
