Sending SMTP email via our website error 535 5.7.139 Authentication unsuccessful

Question

We're sending email from our website via SMTP using ******@ourcompany.com.

We are using these settings to send email:

MAIL_MAILER=smtp  
MAIL_HOST=smtp.office365.com  
MAIL_PORT=587  
MAIL_USERNAME=******@ourcompany.com  
MAIL_PASSWORD=xxxxxxx  
MAIL_ENCRYPTION=tls  
MAIL_FROM_ADDRESS=******@ourcompany.com  
MAIL_FROM_NAME="NOREPLY"  

MFA is enabled, SMTP AUTH is enabled and we created an App password for ******@ourcompany.com.

Upon sending an email we are encountering an error: 535 5.7.139 Authentication unsuccessful, the request did not meet the criteria to be authenticated successfully.

I already research how to fix this and I saw this question: https://learn.microsoft.com/en-us/answers/questions/512954/535-57139-authentication-unsuccessful.html

I can't set Enable security defaults to No because this account is company wide I want to keep this value to Yes. I just want ******@ourcompany.com only to send emails via SMTP.

Then I saw that I can allow Legacy Authentication only on ******@ourcompany.com via Conditional access maybe this will solve my problem. But when I go to Conditional Access I'm seeing this page:

Our account is not on Azure AD Premium. So we cannot send SMTP email unless our account is on Premium?

Answer 1

You cannot use App passwords for SMTP send, you'll have to disable MFA for the account you want to send with.

Answer 2

Hi @Aris Lacdao

Please refer to this link: Basic Authentication Deprecation in Exchange Online – May 2022 Update

Here are some screenshots from the discussion:

If you would like to use basic auth, it is required to disabled Security Defaults.
Otherwise you may need to use modern auth instead.

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