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I'm implementing an Outlook add-in. All calls to Office.context.mailbox.makeEwsRequestAsync are all failing with 403 forbidden for outlook.com (outlook.live.com) accounts. It works fine for Microsoft 365 accounts (outlook.office.com). The EWS calls I make are "GetItem" (to get messages by id) and "CreateItem" to send messages (with MessageDisposition="SendAndSaveCopy") but the behavior is the same for any EWS call.

Looks very similar to https://github.com/OfficeDev/office-js/issues/4292

Your Environment

Platform [PC desktop, Mac, iOS, Office on the web]: All
Host [Excel, Word, PowerPoint, etc.]: Outlook
Office version number: Online / Outlook for Windows v. 2403 / ...
Operating System: Windows 11 / Mac
Browser (if using Office on the web): Edge, Chrome, Firefox

Expected behavior

Office.context.mailbox.makeEwsRequestAsync call is successful for outlook.com accounts

Current behavior

Office.context.mailbox.makeEwsRequestAsync call fail for outlook.com accounts

Steps to reproduce

Call Office.context.mailbox.makeEwsRequestAsync from an Outlook add-in with an outlook.com (outlook.live.com) account

Link to live example(s)

Provide additional details

Context

Useful logs

This is what I see happening in the browser console

A 1st POST call to https://outlook.live.com/owa/0/service.svc?action=GetClientAccessToken&UA=0&app=Mail&n=69 works fine

A 2nd POST call to https://outlook.live.com/owa/0/service.svc?action=ExecuteEwsProxy&UA=0&app=Mail&n=70 fails with the following response:

{
"WasProxySuccessful": false,
"ErrorMessage": "The remote server returned an error: (403) Forbidden.",
"StatusCode": 0,
"StatusDescription": null,
"Body": null
}

OfficeDev / office-js

Outlook Addin Office.context.mailbox.makeEwsRequestAsync calls are failing with 403 forbidden for outlook.com accounts #4353