Hey Rick,
I must have missed your other thread - because I've been trying to chime in on any others that I've noticed where people are seeing the same memory leak that I have been. Since earlier today, I have had Mail running without issue, although I did make some minor tweaks to my mail preferences and have gmail off entirely. Try turning off mail accounts one at a time and see if it stays stabile. If not, delete the account and see if that changes anything.
Right now I have 2 IMAP accounts for work and iCloud running. I noticed syncing issues with drafts and have unchecked syncing drafts with server, which may have solved some of the issue. I'll play around more tonight to see if I can nail down where the issue is.
Also, when you're running Mail, you might want to have Activity Monitor running side by side and when you see the leak start and you're in the 20+ gb's of ram being used, you can force quit Mail through Activity Monitor, which will keep the other Apple apps from crashing (usually).