"On My Mac" header is missing in Mail but the subfolders are intact.

Create a new "On My Mac" mailbox and it should appear.

Quit Mail. Force quit if necessary.

Back up all data before proceeding.

If you're running OS X 10.11 ("El Capitan") or later, triple-click anywhere in the line below on this page to select it:

~/Library/Mail/V3/MailData

If you're running an older version OS X, use this line:

~/Library/Mail/V2/MailData

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. Paste into the box that opens by pressing command-V, then press return.

A folder window will open. Inside it there should be files with names as follows:

Envelope Index

ExternalUpdates.storedata

Move those files to the Desktop, leaving the window open. Other files in the folder may have longer names that begin as above. Move those files, if any, to the Trash.

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. Typically, the process takes a few minutes, but it may take hours if you have gigantic mailboxes. In that case, you may be able to speed things up by temporarily adding your home folder to the Privacy list in the Spotlight preference pane. Remove it when Mail has finished importing.

If the import operation stalls or fails with an error message, quit Mail, delete the two new index files (keeping the original ones that you moved to the Desktop), and try again. According to many reports, the second attempt may succeed after the first one has failed.

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

Back up all data before proceeding.

Step 1

If Mail crashes or freezes immediately on launch, try the steps suggested on this page. Sometimes a corrupt message on a mail server can be deleted by logging in to the server through its web page. If Mail still won't launch, or if you can't take Step 2 for any other reason, skip to Step 3.

Step 2

There are three types of mail account: IMAP, Exchange, and POP. You can determine the type of each account by opening the Mail preferences window, selecting the Accounts tab, and then selecting Account Information.

Select all POP mailboxes, if any, and then select

Mailbox ▹ Export Mailbox...

from the Mail menu bar. Export the POP mailboxes to the Desktop folder.

If you have IMAP or Exchange accounts, and you don't store sent, deleted, and junk messages on the server, export those mailboxes the same way. You can determine whether the messages are on the server by selecting Mailbox Behaviors in the Accounts tab.

Also export all mailboxes in the On My Mac category.

You don't have to export the other mailboxes, because the messages are stored on the servers.

Quit Mail.

Step 3

In System Preferences, open Internet Accounts (OS X 10.9 or later) or Mail, Contacts & Calendars (OS X 10.7 or 10.8). Make notes of the settings for each mail account (all types), then delete the accounts.

Step 4

In the Finder, hold down the option key and select

Go ▹ Library

from the menu bar. Move the following items (some may not exist) from the folder that opens to the Desktop:

Application Support/AddressBook/MailRecents-v4.abcdmr

Containers/com.apple.corerecents.recentsd

Containers/com.apple.mail

Containers/com.apple.MailServiceAgent

Containers/com.apple.share.Mail.compose

Mail

Note: you are not moving the Mail application. You’re moving a folder named “Mail.”

Step 5

Launch Mail. It will behave as if you were setting it up for the first time. Go through the setup process with one account, using the information from Step 3. Test. If Mail works now, recreate the rest of the accounts (if you have more than one) and other settings.

Any custom stationery that you created may be lost. Ask for instructions if you want to preserve that data.

If there’s no improvement, quit Mail and put back the items you moved to the Desktop, replacing any newer ones that may have been created in their place. Stop here and post your results.

Step 6

If you took Step 2, import the mailboxes you exported:

File ▹ Import Mailbox...

Select Apple Mail as the data type. Typically, the process takes a few minutes, but it may take hours if you have gigantic mailboxes. In that case, you may be able to speed things up by temporarily adding your home folder to the Privacy list in the Spotlight preference pane. Remove it when Mail has finished importing.

The mailboxes that you didn't export in Step 1 should synchronize automatically with the server. Again, if the mailboxes are very large, downloading them may take quite some time, and network performance will be slower than usual during that time.

If you skipped Step 2, look inside the Mail folder on the Desktop for a subfolder Mail/V2/Mailboxes. Import the mailboxes it contains.

Test. If Mail is still working, delete the items you moved to the Desktop in Step 4.