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 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.
Examples:
https://contact.faircode.eu/?product=fairemailsupport
https://www.aqua-mail.com/forum/index.php?action=recent
Can somebody please look into this, or contact an engineer at Microsoft?
38 Replies
Hi please this is a helpful discussion below, but MTC is not technical support, so you need to contact Microsoft support directly.
https://answers.microsoft.com/en-us/msoffice/forum/all/535-573-authentication-unsuccessful/cd915151-ae89-4505-8ad3-29680554e710
Deleted 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 smtp.office365.com for personal accounts"
This is a common error and sometimes it is worth reading the shared thread in its entirety
Best regards
