SMTP XOAUTH suddenly failing for Outlook personal with '535 5.7.3 Authentication unsuccessful'

Occasional Contributor

Please see here for the details:


Note that this is about personal accounts for which SMTP AUTH cannot be disabled, and that this worked fine for existing setups/configuration until the end of January.


In other words, this is not something which can be resolved by changing configurations or software, and therefore is rather likely a problem with the Outlook SMTP server.



4 Replies

I also confirmed that until now it is not working.

535 5.7.3 Authentication unsuccessful [ 2023-04-14T01:41:59.958Z 08DB3BD5C46109BA]

I am using offline_access and SMTP.Send as scope via Device Code Flow
These are the endpoints that I used to get exchange device code for an access token to be able to send email using consumer accounts using oauth2

device_endpoint = "",
token_endpoint = ""

Yes, it seems there was a mystery fix happened on MS side. :)
Anyway, due to this issue I was able to produce a Test Tool written in Rust Programming Language just to test this workflow.