Mail Preference keeps changing since High Sierra Update

I finally resolved this on my own. I had to delete the correct preferences file. It is here:

/Users/{your username}/Library/Containers/com.apple.mail

It is actually a folder. This seems to be the modern method Apple uses for preferences.

Try this:

First:

Quit Mail.

Go to this location and delete the com.apple.mail.savedState folder:

~/Library/Saved Application State/com.apple.mail.savedState

Then:

Remove Container file Mail:

Quit Mail.

In the Finder, select Go, then Go to Folder. Copy and paste the path below and hit GO:

~/Library/Containers/com.apple.mail

Move the whole com.apple.mail folder to the Trash, and open Mail and test. If all goes well, you can empty the trash. You may need to re create your user settings.

If there is a problem or you wish to restore the old file, first, Quit Mail.

Then open the Trash. Right click on the folder and choose Put Back from the menu.

I was also having this issue after upgrading from Mavericks to High Sierra (yeah, big jump!). It was not only happening for Mail but other apps, it was basically forgetting the preferences and some settings from Mavericks were not moved over. I just completed a NVRAM reset and mail seems to be ok and so do my other apps now.

To complete the NVRAM reset do the following...

• Quit all apps
• Shut down the Mac
• Unplug for a minimum of 30 seconds, coffee or bathroom break is best 😉
• Power on the Mac and hold down Command + Option + R + P (YES, all 4 keys at the same time) as soon as you power on. Continue holding the keys through the first beep (if we can even call it that) and DO NOT let go until you hear a second beep. All done!

You will instantly notice your screen brightness reset, proving the NVRAM reset is complete.

Hope this helps, best of luck.

This Apple article might help - How to reset NVRAM on your Mac - Apple Support

P.S. I don't have a 10.13.2 update available yet... Do you?

Not only the classic view, but also other settings such as the frequency to check incoming mails, location to save attached files, using bold font for unread mails and plain text for message format, are all reset and changed back to the default. So this is apparently a bug rather than Apple’s conspiracy (^^

With me it has started after applying High Sierra and still contines even after 10.13.1 update, but I think I have found a workaround to minimize its inconvenience.

Until recently, every time the Mail settings changed back to default, I set it up again as I want, which was very irritating. But once, when I just quit Mail and restarted it rather than resetting it, my original settings came back ! Just restarting the Mail app is much easier and less time consuming than totally resetting it.

Next time you encounter the bug, please try this and check if it also works for you.

When you encounter the unintentional pref change, what if you immediately quit Mail app and restart it, rather than resetting its pref ? In my environment, it restores my original setting.

Had the same bug. Running Onyx.app (Automation tab with all checked) seems to resolve this.

Always do a backup before running Onyx…

Same here. 10.13.2 seems to have fixed the Mail bug (for now).

Since I updated my system to the newly released 10.13.2 this morning in Japan time, the preference reset has not happened for more than 12 hours. I could be wrong, but the bug may be finally gone.

Please report here if someone encounters the bug even after applying 10.13.2 update.

The version number of Mail.app is now 11.2 (3445.5.20).

Instead of resetting Mail app each time, try "quit & relaunch" it.

For me, it restores my original settings for the time being.

With the most latest update it took care of my preference issue. Still can't slide emails to my folders to save