When updating to the Mac OS High Sierra Beta my computer hung. I let it run for a long time, but was unable to get it to continue. I restored from a backup, but it did not have all of the files for my email. I had to re-enter my email accounts and restore messages manually. Somewhere in the process, Mail app stopped being able to display the Preferences Pane. I added a new user to my Mac and the Preferences Pane showed up fine, so it looked like something in my user preferences was either missing or corrupted. I removed various things from ~/Library/Preferences/com.apple.mail but nothing fixed the problem. Then I stumbled on a StackExchange mentioning that some things are stored in ~/Containers.
Sure enough, removing Container.plist from com.apple.mail caused Mail to regenerate whatever is in that file. I now get all of my preferences back and they appear to be the same as before the crash.