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I'm struggling to set up an outgoing mailserver with Office 365 using oauth as described in the docs.


Normally, O365 uses port 587 & STARTTLS. When I click test, then I see this error message:


Invalid Operation
An option is not supported by the server: STARTLS extension not supported by server 


So I change it to SSL/TLS and I got this error which contradicts the previous one.


Invalid Operation
Incorrect Connection Security for Outlook mail server "outlook". Please set it to "TLS (STARTLS)".

So in the end, I tried port 465 & STARTTLS which leads to a timeout (which is excpected as to my knowledge O365 doesn't support this).

Has anyone succeeded to succesfully setup outgoing mailservers with O365? 


Fyi:

  • I'm using smtp.office365.com as server
  • Firewall is set up accordingly
  • Incoming mails are working 



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Best Answer

Hi,

what do you use as SMTP server domain?

are you sure SMTP server supports STARTTLS on the M365 side?

Are you able to pass the Oauth approval steps and fetch the token through the App you have created in Entra ID?

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