Return Back to main SMTP notification service option
To fix the error 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant. Visit https://aka.ms/smtp_auth_disabled for more information
ΒΆ Enable the authenticated client SMTP submission (SMTP AUTH) in Exchange Online
To verify that you've enabled SMTP AUTH for a specific mailbox, do any of the following steps:
- In the Microsoft 365 admin center: Go to
Users>Active users> select the user > clickMail> clickManage email apps - Verify the value of Authenticated SMTP (checked = enabled).