Mail.
Try setting up another admin user account to see if the same problem continues. Please post back on whether or not this worked. Also try the Safe Mode. Please post back on whether or not this worked.
Isolating an issue by using another user account
Safe Mode - About
Safe Mode Startup – El Capitan. also Sierra
If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.
Etrecheck – System Information
Desktop
Might be a corrupt .plist.
Do a backup, preferably 2 backups on 2 separate drives.
Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library. Then go to Preferences/com.apple.finder.plist and com.apple.desktop.plist (depending on your OS version, this .plist may not exist). Move the .plists to your desktop.
Re-launch Finder by restarting the computer and test. If it works okay, delete the plists from the desktop. Then reset your preferences as desired.
If the same, return the .plists to where you got it from, overwriting the newer one.
Thanks to leonie for some information contained in this.
