[at]trevor
Your description of how greylisting would work is exactly how Sneakemail does it. The difference is, IF I CHOOSE TO DO SO, I can look at the three views in Sneakemail and see what is happening with any mail at each stage of the greylisting process. That approach won't bother your people that don't care what happens to the mail.
And that approach doesn't mean I won't lose legitimate mail, it just means I will be able to KNOW that I lost it. That gives me an opportunity to contact the mail owner and let them know I didn't receive it, and make other arrangements. The sender probably can't contact me, when he/she receives the bounce, because all they have is an email address for me and it isn't going through. I have to be able to contact THEM.
In the case of Sneakemail which uses multiple receiving email addresses, I can simply turn off greylisting for that receiving email address until my legitimate sender's server issues are resolved. A good point raised by UltraJoe is to have the SpamCop greylisting ignore addresses already on the whitelist. This would serve pretty much the same function as being able to selectively turn off the greylisting processing.
The other bells and whistles mentioned such as editing email addresses, etc. would certainly be nice, but if I could just have the same views as Sneakemail and know that a greylisted mail failed (and why) and then whitelist the sender, that would be good enough control for me to use the feature.
Thanks and regards,
--appyface