"5.7.139 Authentication unsuccessful, account locked." from Outlook SMTP gateway

Eugene K 0 Reputation points
2024-04-02T01:41:00.6166667+00:00

I use gmail to send my @hotmail.com emails through smtp-mail.outlook.com.

Periodically, I am getting

"5.7.139 Authentication unsuccessful, account locked. Contact your administrator."

response from outlook.com's SMTP gateways forwarded to me by Gmail.

This does not happen for every email. Only sometimes.

Plus, I can log in into outlook.live.com and see my email with no problem.

So, my account is not fully locked.

Requesting help on how to fix this.


Another possibly related issue is that a couple of times I tried to ReplyAll to an email thread with about 50 recipients and got NDR receipts on all the recipients. I read somewhere that nowadays Outlook imposes a 100 recipient/day limit on the use of SMTP gateway but I don't think I ever went over it.

Thank you in advance -- Eugene

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  1. SokiGuo-MSFT 22,921 Reputation points Microsoft Vendor
    2024-04-02T07:54:27.49+00:00

    Hi @Eugene K

    Does the problem happen on the Outlook client?

    How did you configure the account?

    According to the error message, there may be other two possible causes of this issue. Please refer to this link and check point 3 (Azure Security Defaults) and point 4 (Conditional Access policy): Error: Authentication unsuccessful.

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