Mail Preference keeps changing since High Sierra Update
Since the update to High Sierra, a Preference I set in Mail keeps changing itself.
I prefer the Classic Layout which is chosen from Mail > Preferences > Viewing and this takes effect correctly when I set the Preference, but it keeps dropping out every third or fourth launch so Mail reverts to the modern layout. Anybody else seeing this?
iMac (27-inch, Late 2012), macOS Sierra (10.12.6)