Rebuild the Mailbox & Reindex Messages to Fix Common Problems in Mail App for OS X
The Mail app bundled with Mac OS X is an excellent email client, but if you have a giant mailbox that has been in use for a long time you may encounter some peculiar problems with sluggishness, message content issues, and searching irregularities. Usually these issues are of distinct types; search errors where some messages don’t come up in results when you know they should, unusually slow behavior when performing mail searches, or just general mail content problems, where an opened message appears blank, incomplete, corrupt, or is otherwise displayed improperly.
Fortunately these issues are very easy to correct thanks to a two step process of forcibly rebuilding the mailbox, and then forcibly reindexing all messages contained within the OS X Mail app.
Before proceeding, you may wish to consider clearing out the Spam/Junk mail folders contained in Mail app to help speed up both reindexing and rebuilding. Such junkmail housekeeping can become automated with a simple settings adjustment as described in this collection of great tips for Mac Mail.
Rebuilding the Mailbox
Rebuilding a mailbox in Mail for OS X is very simple:
- Launch Mail app and pull down the Mailbox menu, then choose “Rebuild”
(If you don’t see the Rebuild option or it is greyed out, close any compose windows and select the inbox in the primary Mail app window)
This rebuild process can take a few minutes, or even an hour or more depending on how large your inbox and sent messages folders are.
An important note: this may cause significant bandwidth use for mailboxes configured with IMAP or Exchange, because the locally stored messages are removed and then redownloaded from the remote mail server. That can make this task unsuitable for users who are connected to the internet using a data capped connection, like a smartphone with hotspot.
Repair & Reindex All Messages in Mail app
You may encounter an alert from Mail app telling you that the mailbox must be repaired, but you can also do this manually. This is particularly helpful if the search functions of the Mail app have become unreliable.
- Quit out of Mail app and go to the Finder
- Hit Command+Shift+G and go to the following path:
- Delete every file that begins with “Envelope Index” (optional but recommended: back up these files to the desktop just in case something goes awry)
- Close the MailData window, then relaunch Mail app to force reindexing
Like rebuilding the mailbox, the reindexing process can also take a while, depending on how large the mailbox is and how much mail is stored on the computer. Be prepared for a lengthy re-indexation if you have tons (thousands+) of messages in Mail app. When finished, try the search or perform the task that you had issues with before and things should be working as usual again.
These two solutions will fix most common mailbox related issues encountered in OS X Mail, so try them out the next time Mail app is performing strangely. On the mobile side of things, iOS does not have similar forced rebuilding and reindexing options, and thus to resolve similar issues you often have to remove the account from iOS Mail settings and then re-add it to resolve like problems, but that’s a topic for another article.