Upgrade to Mountain Lion broke my Mail.app. HELP?

You need to restore OS X.

Restart your Mac while holding down the Command + R keys. From there you can access the built in utilities to restore.

Read before proceeding > OS X Recovery

Backup all important files before performing a restore just in case.

Best to never interupt a system process when updating software.

Quit Mail. Force quit if necessary.

Back up all data. That means you know you can restore the Mail database, no matter what happens.

Triple-click anywhere in the line below on this page to select it:

~/Library/Mail/V2/MailData/Envelope Index

Copy the selected text to the Clipboard (command-C). In the Finder, select

Go ▹ Go to Folder

from the menu bar. Paste into the box that opens (command-V), then press return.

A Finder window will open with a file selected. Move the selected file to the Desktop, leaving the window open. Other files in the folder may have names that begin with "Envelope Index". Move those files, if any, to the Trash.

Log out and log back in. Relaunch Mail. It should prompt you to re-import your messages. You may get a warning that the index is damaged and that Mail has to quit. Click OK.

Test. If Mail now works as expected, you can delete the file you moved to the Desktop. Otherwise, post your results.

You didn't follow his instructions.

Open the Library folder in your home folder by holding down the option key and selecting

Go ▹ Library

from the Finder menu bar. Navigate in the usual way to the folder indicated above.

Launch the Console application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Console in the icon grid.

Make sure the title of the Console window is All Messages. If it isn't, select All Messages from the SYSTEM LOG QUERIES menu on the left. If you don't see that menu, select

View ▹ Show Log List

from the menu bar.

Click the Clear Display icon in the toolbar. Then try the action that you're having trouble with again. Select any messages that appear in the Console window. Copy them to the Clipboard (command-C). Paste into a reply to this message (command-V).

When posting a log extract, be selective. In most cases, a few dozen lines are more than enough.

Please do not indiscriminately dump thousands of lines from the log into this discussion.

Important: Some private information, such as your name, may appear in the log. Anonymize before posting.

Back up all data.

1. Triple-click the line below on this page to select it:

~/Library/Mail/Bundles

Services ▹ Open

from the contextual menu. A folder may open, or you may get an error message that the item can't be found. Either result is normal. If the folder does open and has contents, move the contents to the Desktop. Relaunch Mail and test. If there's no change, put the contents of the folder back and quit Mail again.

2. Repeat with this line:

/Library/Mail/Bundles

This time you may be prompted for your login password when you remove the items. Make sure they're removed from the folder and not just copied to the Desktop. If necessary, copy them first and then move the originals to the Trash.