Our service is connecting to https://outlook.office365.com using EWS on behalf of an @outlook.com user. We're getting status 403 and the header X-BackEndHttpStatus : 403.
What does it mean?
EWS connections seem to work for other @outlook.com users just fine.
Thank you.
Update Apr'19: What we see is that EWS for @Outlook.com accounts is refusing connections from Heroku/AWS IP addresses. Not sure why.
According to my search, do you have a Authentication with your EWS application.
You could make a authentication with the below link:
Authenticate an EWS application by using OAuth
EWS must have the "Full access to user's mailbox" permission.
If your Outlook account has multi-factor authentication, please refer to this link:
Set up multi-factor authentication for Office 365 users