Why am I receiving an "Invalid login: 535 5.7.139 Authentication unsuccessful" error for my Microsoft account?

If you encounter the error message "Invalid login: 535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant.", it indicates that SMTP Client Authentication is disabled for your account. Microsoft disables this setting by default.

To resolve this issue, you need to enable SMTP Authentication for your account. For detailed instructions on how to do this, please refer to our step-by-step guide:

https://help.pipl.ai/en/articles/8666007-how-to-connect-your-microsoft-365-business-email-accounts