Intended Audience: People experiencing Authentication Failure with Outlook 2016 for macOS and O365. Symptoms: Outlook 2016 for macOS stopped being able to connect to O365 and check mail, no error displayed at this stage. Credentials are definitely correct, still able to access O365 mail via iOS app and browser. Deleting and re-adding the account within Outlook
I wanted to quickly share a tweet from Tweetbot to a friend by email, I was surprised when “Apple Mail” launched and asked me to setup an email account, I do not use “Apple Mail” I was using Airmail as my primary email client at the time.
What should have been a quick change of settings turned into a 10 minute battle with El Capitan to change the default mail client!