I am having an issue with Outlook 2016 frequently prompting for the username and password for the server: smtp.mail.yahoo.com
It did this when I had the mail setup as POP account on my older PC (Windows 7) - I then purchased a new PC (Windows 10) and setup the email as IMAP and I am still getting this frequent pop up. The username and password are correct. I did not have this issue with previous version of Outlook. Any help you could provide would be appreciated. Thank you.