Mail doesn't want to start anymore

Question

Mail doesn't start. I just get the colourful ball spinning. I have to force it to close down everytime. I've tried to re-install Mavericks, but the problem remains.
What should I do?

Answer 1

These fixes have helped others, depending on the situation.
Have an up-to-date Time Machine or other backup before attempting any major software updates or rebuilds.
For more about backups:
Time Machine Basics: http://support.apple.com/kb/ht1427
Most commonly used backup methods: 
https://discussions.apple.com/docs/DOC-3045
Methodology to protect your data.  Backups vs. Archives.  Long-term data protection:
https://discussions.apple.com/docs/DOC-6031
Make sure your software is up to date.  Apple recently released a Mail update.
Apple > Software Update...
Try booting in Safe Mode.
          Boot and when you hear the bong hold down the Shift key.
          It will boot slowly.  Be patient.
          Login the the user account.
          Restart.
Another fix to try:
Shut down Mail.
Open the Finder. From the Finder menu bar click Go > Go to Folder
Copy and paste the following
~/Library/Mail/V2/MailData/
Click Go.
Move all "Envelope" files to your desktop.
Restart Mail and let it convert/reindex your mailboxes.
If this worked, Trash the Envelope files file that are on your desktop,
if not put them back.
Another fix:
Open the Finder. From the Finder menu bar click Go > Go to Folder
Copy and paste the following:
~/Library/Containers/com.apple.mail/Data/Library/Caches/com.apple.mail/Cache.db
Click Go.
Move the Cache.db file to the Trash.
Restart your Mac and try Mail.
You can try restoring mail from a Time Machine backup.
Hold down the Option key and in the Finder Go > Library
Enter Time Machine.
Select a date before the Mavericks upgrade.
Restore Mail.
Advice from another thread:  https://discussions.apple.com/message/23657222#23657222