by Tobias Lekman, 15 June, 2016
When logging into Exchange or Office 365 using Outlook 2016 for Mac. You receive the error “Authentication failed. Check your account information and try again” or the client simply stops syncing.
I looked around various forums without any response but found that the cause for me was due to invalid KeyChain entries. You need to fix the KeyChain on your Mac by trying one of the following:
Test 1: Reset your iCloud Keychain password
If you are syncing Keychain Access to iCloud then try resetting the iCloud key by
Test 2: Reset default keychain
If this should not work then you may need to reset your Keychain