My mail preferences are blank after I updated my computer. What can I do?
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Dealing with mail prefs is different than it used to be. There's no longer a com.mail.prefs file in the preferences folder of your user library. Now you'll need to look elsewhere. Instead, try moving the following files out of their folders and onto your desktop. Reopen mail and it will rebuild new healthy versions of these files, therefor hopefully solving your mail preferences issue. Restart may be required.

Order of effectiveness

~/user/Library/Containers/com.apple.mail
~/user/Library/Containers/com.MailServiceAgent
~/user/Library/Saved Application State/com.apple.mail.savedState



to get to the user library folder, select Go in the menu and hold down the option key. Remember, always have a good time machine backup before deleting files during troubleshooting.

If you don't understand how to get to the above folder path, you should schedule a session.