POSTMAN Office 365 MailboxNotEnabledForRESTAPI

Installed the Office 365 plugin for POSTMAN SMTP. All looks OK, inclusive Office 365 activation.
But when sending a testmail, I get the following error:

Code: 404, Message: Not Found, Body: {“error”:{“code”:”MailboxNotEnabledForRESTAPI”,”message”:”The mailbox is either inactive, soft-deleted, or is hosted on-premise.”,”innerError”:{“date”:”2023-01-21T09:40:19″,”request-id”:”fa8f6e4d-3ec0-444f-be03-908a2305a98c”,”client-request-id”:”fa8f6e4d-3ec0-444f-be03-908a2305a98c”}}}

The “To:-mailaddress” I use does exist in M365 (it’s my own e-mail address).

I can’t find an answer on the forum/Google so maybe someone here has a good idea?

Thx in advance,
Hans Grundemann.