Macmail - could not load internet accounts preference panes

You are welcome. Have you checked to make sureyour e-mail provider still offers POP accounts?

That is a file name variation.

For System Preferences, click and hold where the arrow in the screen shot is pointing. At the bottom you should see Customize. Select that and see if Internet Accounts is checked.

To reinstall Mail, you have to reinstall the OS.

Delete the account, then add it back. After filling in the 1st screen, hold down the option/alt key while clicking Continue. Fill in the necessary information, then click continue until all screens are filled in.

Manual Setup – El Capitan

Might be a corrupt .plist.

Do a backup, preferably 2 backups on 2 separate drives.

Quit the application.

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.systempreferences.plist. Move the .plist to your desktop.

Restart the computer, open the application, and test. If it works okay, delete the plist from the desktop.

If the application is the same, return the .plist to where you got it from, overwriting the newer one.

Thanks to leonie for some information contained in this.