Cannot access Mail Preferences

If you have installed some anti virus , unwanted apps , cleaners etc uninstall them , after that delete the account by going to system preferences - internet accounts and configure the mail account Set up Mail with email accounts - Apple Support

Ok, did all that, still cannot access Mail Preferences. Do you have another idea?

Take back up of all Data , erase the HD and reinstall the OS , can also try new user account and configure mail app .