Not certain, but this can fix myriad Mail problems...
Safe Boot from the HD, (holding Shift key down at bootup), it will try to repair your Disk Directory while the spinning radian is happening, so let it go, run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, then move this folder & file to the Desktop.
Move this Folder to the Desktop...
Move this file to the Desktop...
If that doesn't do it and you can afford to redo all your Rules, try these & reboot...
Note, in 10.5 & up /Users/YourUserName/Library/Caches/Mail/ may or may not exist.
Thanks, I went thru it, ran the safe boot, disk utility, moved the mail caches, then got a little lost on the last Message/rules redo. What do I do with those? I can still get a workable new message window in Mail but the message viewer window is blank, and it will not quit, must force quit.
What do I do with those?
I doubt that's a problem, but with Mail not running you can move them to the Desktop.
I can still get a workable new message window in Mail but the message viewer window is blank...
Hmm, in Mail>Preferences>Fonts & colors, try changing the fomts used & see if that makes any diff?
Intead of reinstall, try applying the big Combo update, which includes Mail...
The combo update for Intel-based Macs...
Repair Permissions afterwords, reboot.
If worried about loosing any emails, On Mail...
First Quit Mail, then I'd backup these two Mail folders, by right clicking on them in the Finder, then choose Archive/Compress.
(Could be a different folder here if you chose such in Mail Prefs)
Right click on that Mail folder, choose archive, you'll get everything in the folder, and the folder itself in a file called Mail.zip, move it to a safe place, same for the Mail Downloads folder... only the plist is separate.