Mac Mail Generates Beachball

Question

My Mac Mail regularly generates a spinning beach ball when I right click a message (typically to move it to a folder On My Mac), and I need to Force Quit to exit the app.  I am currently running Mavericks 10.9.4, but the problem has existed in previous Mavericks versions.  I am running a Mac Book Pro with 8Gb RAM and 256Gb solid state drive, 2.8GHz Intel Core i7.  I have no solution other that Force Quitting and sending error messages to Apple.

Answer 1

Please follow these directions to delete the Mail "sandbox" folders. In OS X 10.9 there are two sandboxes, while in 10.8 there is only one. If you're running a version older than 10.8, this comment isn't applicable.
Back up all data.
Triple-click anywhere in the line below on this page to select it:
~/Library/Containers/com.apple.mail
Right-click or control-click the highlighted line and select
          Services ▹ Reveal
from the contextual menu.* A Finder window should open with a folder named "com.apple.mail" selected. If it does, move the selected folder—not just its contents—to the Desktop. Leave the Finder window open for now.
Log out and log back in. Launch Mail and test. If the problem is resolved, you may have to recreate some of your Mail settings. You can then delete the folder you moved and close the Finder window.
This action will delete any custom Mail stationery that you have created. If you want to preserve it, ask for instructions.
If you still have the problem, quit Mail again and put the folder back where it was, overwriting the one that may have been created in its place. Repeat with this line:
~/Library/Containers/com.apple.MailServiceAgent
Caution: If you change any of the contents of the sandbox, but leave the folder itself in place, Mail may crash or not launch at all. Deleting the whole sandbox will cause it to be rebuilt automatically.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination  command-C. In the Finder, select
          Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.