After upgrading to Mountain Lion several users have reported that their computer often crushes to a halt when running the Mail application. In these users we have discovered a common error that when fixed will return to your system to normal speeds.
Charlie recently dropped us the following question:
“I recently updated to OS X 10.8 Mountain Lion and noticed that my system would hang when running the Mail Application. The CPU through the Activity Monitor would seem to spike repeatedly for Mail but would never peg out at 100%. In searching the console for errors, I found that Mail was reporting a frequent deny-file-read-data error for com.apple.mail.plist file. I tried to correct permissions without success. Any recommendations?”
In exploring this issue, we found a similar error message on multiple systems:
sandboxd: Mail deny file-read-data /Library/Preferences/com.apple.mail.plist
When this plist file was examined, it typically contained nonessential data. Often the file had not been modified in over a year. Deleting this plist file had no obvious consequences, and removing the file caused the frequent error message and Mail slowdowns to resolve.
We safely removed it on a couple of machines with success without any negative consequences; however, proceed at your own risks.
Do you have this error?
When mail seems to be hanging, open spotlight and type in console to run the application. If this issue is affected you, you should see something similar to the following listed multiple times in your console messages:
If you see this error, then proceed.
Removing the plist file
1. Close the Mail application.
2. Open Finder. Click the Go menu and then select Go to Folder.
3. Enter the error plist file location /Library/Preferences/com.apple.mail.plist here.
4. Right-click the selected file and move to trash.
5. Open the Mail application. If something appears broken, drag the deleted file back out of trash into its original location. Otherwise, if everything is running correctly, the error should be corrected. Periodically check the console application to ensure that the com.apple.mail.plist error has not recurred.
I suspect that this file is byproduct of upgrading the Mail application over a prior version. Alternatively, it may have been an incompatible Mail plugin that became broken upon the update. Either way, the old date and nonspecific settings in this file have suggested by our testing that it should be safe to delete if you are experiencing this error.