Knmlee, I tried virtually all the solutions discussed on the board, including deleting and rebuilding my exchange account multiple times...at first, Outlook worked while Mail didn't, but that went south pretty soon, too...after that I tried AirMail...worked for about a week, then it would no longer automatically get email from the server--had to restart the program to get mail. At the same time, kernal_task was swelling to nearly 5 gigs, causing me to have to restart the machine several times a day due to no operating memory, even when no programs were running.
I finally deleted my exchange account, then deleted accounts.plist, then re-added the exchange account.....once I did that, the memory problems I was having went away and my emails downloaded just fine...
randyKates, I have roughly a third of the messages you have, so that could certainly be a factor...