Some ISP are already filtering port 25 for all customer and will unlock it on request (AS44885 to only name one I know). As far as I heard, it is the cheapest, most efficient way to do this with best results and it does not tackle the "oh-don't-touch-my-privacy" issue that I understand anyway.

Please reconsider this setup and just block port 25 instead of doing
this inspection.

Let's be savvy. That is the best option for everybody. It is just funny to notice that it is always the same people that will suffer from spam and it will always create profits for others, not only spammers, but also people that can sell products and services to fight against - think of the millions Postini, MXLogic, Messagelabs, Ironport, Websense and all other AV/AS/App. solutions made out of that.

Yep, I hate the privacy implications. But with 100k abuse complaints/month
- what would you do, besides going postal?

Let's find good in bad. At least this creates work. Just think about the whole project lifecycle: projects manager -> quality committee -> PR/marketing -> designers -> network team and -> first-line support staff.

Gregory