This is because Apple has integrated a function that could be interesting in the application Mail, that is, to complete the field Surname of our contacts intelligently, but in most cases this means duplicating the name field. After months of research I finally found the solution that I want to share with you. The procedure to do this:
- Start the application Mail and go to the men bar, in Window -> Previous recipients
A window will open with all the addresses to which you have sent an email. This is the cause of all the problems.
- Select all the addresses present and click on the button Remove from the list
- Now close the application Mail by pressing the keys cmd + Q and start the application Terminal present in Applications -> Utility
- Copy the following string, paste it into the Terminal and hit enter
defaults write com.apple.mail SuppressAddressHistory -bool true
By performing these simple steps you will definitively solve the problem of duplicating the name in the contacts on your Mac.