"Authentication unsuccessful", SMTP, basic auth, Microsoft 365 email

Question

"Authentication unsuccessful" while sending email with Microsoft 365 email using SMTP with basic auth

Answer 1

• Disable "Security Defaults": Microsoft Entra > Identity > Overview > Properties. (security defaults are a set of settings that you can enable yourself individually, after disabling the "security default", for example MFA).
• Deselect "Turn off SMTP AUTH protocol for your organization": Exchange Admin Center > Settings > Mail Flow
• If MFA is enabled for the email, create an app password (app passwords cannot be created for Admin emails): Microsoft 365 Admin Center > Active Users > Multi-factor Authentication > In "server settings" tab at the top, make sure "Allow users to create app passwords to sign in to non-browser apps" is selected" > Back to "users" tab, select the email > Enable > Enforce > In a new window login to office.com using the target email address > Follow the instructions to Setup MFA > Click on your profile photo at top-right and select "View Account" > Security Info > Add Sign-in Method > Select "App Password"
• Wait for about an hour for the settings to be activated properly