If you see error 535 5.7.139 Authentication unsuccessful when connecting your Microsoft 365 email, SMTP AUTH is disabled in your tenant settings.
Microsoft 365 blocks SMTP authentication by default for security. You'll need to enable it before MCA Pilot can send emails on your behalf.
Before you begin: Make sure you've already set up your email sender in MCA Pilot. This article only covers fixing the 535 authentication error.
If Your Email is Hosted on GoDaddy
If you're using a Microsoft 365 or Outlook email that's hosted through GoDaddy, you need to enable SMTP authentication in your GoDaddy dashboard instead:
Log in to your GoDaddy account.
Navigate to your email or Office 365 dashboard.
Click Manage next to the user account.
Under Account Information, find Advanced Settings.
Toggle SMTP Authentication to ON.
Click Continue or Save.
Once enabled, return to MCA Pilot and test your connection. If you're still having issues, the steps below may also apply.
Enable SMTP AUTH for Your Mailbox
If you're using a single mailbox, enable SMTP AUTH for just that account:
Go to the Microsoft 365 admin center.
Navigate to Users > Active users.
Select the user account that needs email access.
Click the Mail tab.
Under Email apps, click Manage email apps.
Check the box next to Authenticated SMTP.
Click Save changes.
Changes can take 5-10 minutes to apply. Wait a few minutes before testing your connection.
Enable SMTP AUTH for Your Entire Tenant
If multiple users need SMTP access, enable it tenant-wide using PowerShell:
Install the Exchange Online PowerShell module.
Connect to Exchange Online:
Connect-ExchangeOnlineRun:
Set-TransportConfig -SmtpClientAuthenticationDisabled $falseVerify the change:
Get-TransportConfig | fl SmtpClientAuthenticationDisabled
The output should show False, meaning SMTP AUTH is now enabled.
If your organization uses Azure AD Security Defaults, they may override this setting. You'll need to disable Security Defaults in the Azure Portal under Azure Active Directory > Properties > Manage Security Defaults.
Test Your Connection
After enabling SMTP AUTH:
In MCA Pilot, go to your profile and click the Senders tab.
Hover over your Microsoft 365 sender and click Test Connection.
If successful, the sender status will update to "Verified" with a timestamp. If you still see errors, wait a few more minutes for the changes to propagate, then try again.
Common 535 Error Messages
You may see variations of the 535 error:
535 5.7.139 Authentication unsuccessful, SmtpClientAuthentication is disabled for the Tenant— SMTP AUTH is disabled tenant-wide535 5.7.139 Authentication unsuccessful, user is locked by your organization's security defaults policy— Azure AD Security Defaults are blocking SMTP535 5.7.3 Authentication unsuccessful— Generic authentication failure, usually the same SMTP AUTH issue
All of these are fixed by enabling SMTP AUTH using the steps above.