This is at least the 6th time I've posted on these forums for this same problem. It seems every "expert" has a different diagnosis and a different solution. Here's the problem.
1. I upgraded to Mountain Lion about a year ago.
2. Ever since then, on occasion, Mail slows down to a crawl (or slower).
3. I log on to these forums and find some "solution" or other. Some work, some don't, and some I don't remotely begin to understand (I'm a user, not a tech nerd - I've never used Terminal since my first Mac in 1989).
4. A period of about three months has passed since my last major problem. I've deleted all old (older than today's date) copies of mail.plist. That had worked sort of in the past, but Mail doesn't seem to be creating new copies of this file anymore like it was for a long time after my ML upgrade. Mail is now so slow that switching from one message to another takes upwards of a minute. My fan is making audible noise that it never has before.
5. There is only one copy of mail.plist (that I can find) in my system.
6. I have rebuilt my in-box - zero results.
7. I'm getting REALLY tired of this crap. This is Apple circa 1994, not Apple circa 2013.
8. Does anyone have a REAL FIX for this idiotic problem that doesn't require a computer science master's degree?
I'm dyin' here...