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