Dupliate-ish email search?

I'm mulling over writing some code to find emails in a maildir that are duplicates, ish. That is to say that sometimes the same message doesn't quite show up as an exact match. Like some ad company may send you three identical messages, except they aren't actually EXACTLY identical, the message-IDs are different, and may the to address quoted part is different, so normal duplicate finders fail to find them.

Before I start, is this a solved problem?

-- I thought that they were angels, but to my surprise, we climbed aboard their starship, we headed for the skies.