Not able to send mail from personal Outlook mailbox.

Question

I have created mail and want to send mail from it. I have tried sending the mail using OAuth 2.

But, below mentioned error is encountered.
535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Mailbox. Visit https://aka.ms/smtp_auth_disabled for more information.

I have tried below method, but same error is generated.

1. Disable / Enable multifactor authentication (MFA) on the mailbox.
2. Disable the Azure Security Defaults by toggling the Enable Security Defaults to No.

Also, found below approach, but is not present in personal account.

1. In the Microsoft 365 Admin Center, make sure "Authenticated SMTP" is enabled. (M365 admin center > Settings > Org Settings > Services > Modern authentication)
2. If SMTP authentication is disabled globally, you can enable it for specific mailboxes:

• Go to **** M365 admin center **** > Users > Active users
  • Select the specific user > Mail > Manage email apps
  • Verify the Authenticated SMTP setting: unchecked = disabled, checked = enabled.
  • When you're finished, select Save changes.

Answer 1

Hi Hardik Jogadiya,

Welcome to Microsoft Q&A forum.

The error that you are seeing indicates that the server is rejecting SMTP AUTH for that mailbox.

If this is a personal Outlook.com account (For example: @outlook.com/@hotmail.com), you will not have the Microsoft 365 Admin Center "Authenticated SMTP" switch because those settings apply to Exchange Online tenants.

For personal Outlook.com mailboxes, the supported approach for app/script sending is OAuth2 for SMTP: register the app, obtain access token and authenticate using SASL XOAUTH2 with the scope "https://outlook.office.com/SMTP.Send". 

For your reference: Authenticate an IMAP, POP or SMTP connection using OAuth

If your sending tool cannot do OAUTH2/XOAUTH2, you will need to use Outlook web/app or switch to a client that supports OAuth2 SMTP

For conveniences, please kindly send your domain here on the comment or send via the Private Message.

Thank you so much and I hope you have a great day.

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