Milter-greylist

You might be able to populate a hash or socketmap with your address pairs, have a sendmail check_compat rule set a macro if the map matches, and have milter-greylist check that macro.

I've contemplated something like that, based on webmail "Emailed Contacts" addressbooks, but haven't coded a line. I'd also like a -5 SpamAssassin bump. I'd be interested in dividing the work or at least sharing QA. I can easily handle the sendmail ruleset hack.