My Mail won't set up in Internet Accounts or just from Mail

I have wiped my iMac to pass onto my partner. I am trying to set up Mail but in System Prefs. Internet Accounts when I add the Yahoo email address it ticks for contacts and messages but next to Mail is just a rotating icon. When I click on Calendars the rotating icon appears for a second then it just un-ticks. When I go into Mail and try the message comes up 'Duplicate Account'.