535: 5.7.3 Authentication unsuccessful

Question

Hello,

I have an issue when using an O365 account and sending emails from an application.

The application has been suitable to use tls/starttls, port 587, ect.

When entering an email account and password, the following message occurs:

"535: 5.7.3 Authentication unsuccessful"

I would like to understand, what are the mininal features of an O365 account so that it can be used from another application.

I have performed different tests, which allow me to indicate that the account is Ok.

Thank you.

Answer 1

Hi Marvin,

Thank you for your help.

I write because the inconvenience still persists, our test:

• I login to OWA to validate that the account and password are correct.
• SMTP authentication is enabled.
• Sending mail from Outlook with email account, ok.
• Testing with the following configurations:
  • Server: smtp.office365.com
  • Port: 587 and 25
  • Connection type: starttls
  • User: full email address and without domain
  • Password: configured user
• Checked if IP was blocked

After the checks I still can't send emails from our application. Error message: "535: 5.7.3 Authentication unsuccessful"

Would there be any additional configurations in O365 that I should look at?

Thanks,

Answer 2

Hi All,

please check your MX entry.  It should be like domainname**.mail.protection.outlook.com**

This means as SMTP server use domainname**.mail.protection.outlook.com**with port 25.

I hope this helps.

Best regards

Chris

Answer 3

Hi Chris,

We are getting following error

AuthenticationInvalidCredentials: 5.7.3 Authentication unsuccessful [DB6PR07CA0108.eurprd07.prod.outlook.com]

But the credentials are all correct. We tried with several accounts. 

Best Regards,

Vishwas

Answer 4

Hi Carlos,

From my experience, it could be the SMTP authentication of your Office 365 account hasn't been enabled. The third-party application uses SMTP submission to authenticate Office 365 account. To enable the SMTP auth, you can refer to the following instruction.

Enable or disable authenticated client SMTP submission (SMTP AUTH) in Exchange Online

As a side note, to run the PowerShell commands, it requires an Office 365 admin account to Connect to Exchange Online PowerShell. So if you're not an admin, please contact the Office 365 admin in your organization to help you confirm it.

Regards,

Marvin

Answer 5

Hi Marvin,

We have same issue. The application was sending email till march. The issue started happening from April 2020 it self. 

Please help as soon as possible.

Thanks