Fixing a Common MacOS Mail Bug: Wrong Smart Mailbox Unread Counts and Empty Content

Have you ever found that your Mail app's smart mailboxes are showing the wrong number of unread messages, or worse—are completely empty? 

It’s a frustrating and persistent bug that can be caused by a corrupted Spotlight search index. While rebuilding mailboxes and restarting the app can sometimes help, a more thorough approach is often required. This guide details a tested method to resolve the issue (tested meaning: it worked for me:-), based on real-world troubleshooting.  I sincerely hope it can help others like it helped me.

Note: this was tested on OSX 14.5

The Problem 

For some reason (that I can't easily explain) the OSX system’s Spotlight index can become corrupted, especially for data from the Mail app. 

Smart mailboxes rely on this index to display search results, so if the index is faulty, the smart mailboxes will show incorrect unread counts or even appear empty. Standard fixes often fail, requiring a more complete system-level refresh. 

I don't know about you, but I spent literally days and even weeks figuring this out. Apple support forums did not show anything useful either.

 The Solution

The most effective fix is a complete rebuild of the Spotlight search index. However, for a reliable result, a few preliminary steps are needed to ensure the Mail app is in the correct state, based on my experience. 

1. Temporarily toggle accounts (don't skip this step!)

Do this first to make sure that Mail is in a receptive state before the index is rebuilt! In my case it was a vital part of the solution.

This is best done while the Mail Preferences window is open and closed at specific times to ensure the changes take effect:

1. Open the Mail app
2. Go to Mail > Settings > Accounts. 
3. Select an account. 
4. Uncheck the "Enable this account" option. 
5. Repeat this for all enabled accounts. 
6. Close the Settings window. 
7. Re-open the Settings window.
8. Re-enable the accounts again. 
9. Close the Settings window again. 

Note: closing the Settings window in between things proved to be crucial in my case. Don't skip this.

2. Run a system-wide Spotlight re-index

This is the most critical step. Use the Terminal to force a complete rebuild of the Spotlight index. 

1. Quit the Mail app completely. 
2. Open Terminal (from Applications > Utilities). 
3. Enter the following command and press Enter: sudo mdutil -Ea (enter your administrator password when prompted).

This process runs in the background and can take hours, depending on the amount of data on your Mac. 

3. Wait for re-indexing to finish

WAIT! 

WAIT! 

WAIT! 

You can check the progress of the re-indexing by clicking the magnifying glass icon in the Finder's menu bar and typing some search term. The search results pop-up window will show a progress bar indicating the indexing completeness (if it is still busy). 

Based on what I was told, it is very important that you do not open the Mail app until indexing is finished. Opening Mail too soon can supposedly interfere with the rebuild and lead to incomplete results. 

So just give it some time, it will be time you recover once Mail works again.

4. Restart Mail 

Once the Spotlight re-indexing is complete, you can safely relaunch the Mail app. Your smart mailboxes should now show the correct unread counts and their full content. 

 Summary: 

The key to resolving this bug is performing a thorough Spotlight index rebuild while the Mail app is completely closed. The account toggling and UI refresh steps ensure that Mail is in a receptive state before the index is rebuilt. By following these steps and allowing the system to complete its work, you can get your smart mailboxes back to full working order.