Forum Discussion
SMTP XOAUTH suddenly failing for Outlook personal with '535 5.7.3 Authentication unsuccessful'
Authenticating with XOAUTH is suddenly failing with 535 5.7.3 Authentication unsuccessful for smtp.office365.com for personal accounts (Outlook/Hotmail/Live). It started with a few accounts, but it s...
JeremyTBradshaw did you see this recent issue?
https://answers.microsoft.com/en-us/outlook_com/forum/all/user-is-authenticated-but-not-connected/7d8465ec-9906-4733-8795-8ff75a527d02
Who does still want to use an Outlook account?
Actually no. I'm currently working on learning MailKit usage in PowerShell, but using EXO/M365/Entra to do this, rather than personal Outlook. I just came across this page as I was earlier having the same 535 5.7.3 Authentication Unsuccessful error. I got past it, and it was unrelated to your original issue's solution. But couldn't help but notice how you were getting actively deflected and want to let you know I could see that and thought it was ridiculous.