Some Microsoft accounts may have 2FA enabled, this requires them to connect via an APP password.
If 2fa is enabled then you will receive the following response.
Please check your email address and password.
If you are connecting an iCloud / Yahoo / AOL account or
have two-factor authentication enabled, you will need to
create an app password and use that.
Learn more about App Passwords.
If your credentials are correct, you may need to enter extra
information under ‘Advanced Settings’.
As the developer you will find the following response in the Nylas Dashboard Auth & API logs:
Event: Exception happened while creating or updating EWS account
Error message: Wrong username or password for https://eas.outlook.com/EWS
NOTE: You can not view the email address of the account that tried to authenticate.
You can check on the Microsoft Security page to determine if 2FA is enabled, this is also where you generate an app password.