When using OAuth, the email address used to authenticate must remain the same throughout the process!
- Make sure you´re not entering or selecting a different email address on Office 365 than was originally entered on Nylas.
- Make sure you´re not attempting to log into an alias. You must authenticate with the main account.
- If the issue persists, log out of all Office365 accounts, and then try again.
- Alternatively, try authenticating from an Incognito or Private browser session.