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

Copper Contributor

Authenticating with XOAUTH is suddenly failing with 535 5.7.3 Authentication unsuccessful for for personal accounts (Outlook/Hotmail/Live). It started with a few accounts, but it seems more, and more people are suffering from this.


To be clear: authentication worked fine before for the same account. It just stopped working, with the same OAuth refresh token, but only for the SMTP server, not for the IMAP server. Authenticating with an (app) password for the same account is a workaround for this issue, so it is probably not an account status problem.


Normally "535 5.7.3 Authentication unsuccessful" means that SMTP AUTH is disabled, but this is not possible for personal accounts, as far as I know.




Can somebody please look into this, or contact an engineer at Microsoft?



35 Replies


Hi please this is a helpful discussion below, but MTC is not technical support, so you need to contact Microsoft support directly.

535: 5.7.3 Authentication unsuccessful - Microsoft Community

@A1-A1 Thanks, but that's about Office 365 accounts with SMTP AUTH disabled, but this issue is about personal accounts (Outlook/Hotmail/Live).


So, it is not the same issue.


Moreover, this problem does not occur for Office 365 accounts in the same setting.


"535 5.7.3 Authentication unsuccessful for for personal accounts"


This is a common error and sometimes it is worth reading the shared thread in its entirety

Best regards

@A1-A1 I did my research before posting here. Believe me, those articles won't help to solve this problem. Quite some people using multiple apps are suffering from this, and all of a sudden. Therefore, this is likely a problem at the side of Microsoft, again, unfortunately.



" Therefore, this is likely a problem at the side of Microsoft, again, unfortunately"

I understand, but it is complicated and rather this post - will be another submission.

Enable or disable SMTP AUTH in Exchange Online | Microsoft Learn

Please this is official documentation.




So, what do you propose to do? Contact Microsoft? If so, how? There doesn't seem to be a support contact for Outlook/Hotmail/Live, so ...

@A1-A1 This is about personal Outlook/Hotmail/Live accounts, so the Office 365 team won't help.

Please follow your own link, select "Microsoft 365", select "Home", and you'll see that there is community support only.
I have selected "Business" and submitted case 2302061420000077.
Let's see what happens.


Microsoft Apps

Check if this app provides proper synchronization - this is the easiest way and almost always works :)

The Outlook app will work, no doubt, but this is not about the Outlook app. Moreover, the Outlook app is not suitable for all purposes.


This is built in for Windows - install and write!

Please understand that not everybody uses Windows. For example, I do not.


Thank you for the discussion was very informative!

@A1-A1 I told you so:


"Concerning your service ticket, I wanted to inform you that we support only enterprise accounts since we are Exchange Online break-fix team."


What do you suggest as an alternative?



And what system do you want to sync mail on?

Do you use Edge?



Do we have any solution so far. We are facing same issue. Suddenly, SMTP OAuth stopped working for personal accounts for last few days. IMAP is working fine. We use limilabs library for IMAP and SMTP. Following exception is being thrown:

Authentication unsuccessful [YT3PR01CA0065.CANPRD01.PROD.OUTLOOK.COM 2023-02-07T18:12:16.786Z 08DB090770EF088C]