I'm not able to open mail preferences, mail locks up.
After updating to Mountain Lion Mail stop working properly. When I try to open preferences the software locks up. Rainbow wheel stay forever.
iMac, OS X Mountain Lion, Mail
Bootup holding CMD+r, or the Option/alt key to boot from the Restore partitiion & use Disk Utility from there to Repair the Disk, then Permissions.
Re-install if that doesn't work.