Sounds like your OS and/or mail application has some file corruptions. Hopefully its just a Btree/FAT file table error. If not your HD maybe going bad.
You may need to reformat the HD and re-install the OS & apps. Do you have an external firewire HD with which to backup your files onto and make as a bootable volume? If so yo could try using it as your boot disk and run Disk Warrior again. If that fails you need to reformat the disk and run the disk tests for a while to make sure the drive is OK.