Question 181120 in ASP.NET Question posted in
The official documentation can be found here.

Asp.net – The SMTP server requires a secure connection or the client was not authenticated.(535 5.7.3)?

I am totally fed-up with Office 365 SMTP configuration, I have done all requirements to send email using my account on Office 365, and always giving me the same error message :

The SMTP server requires a secure connection or the client was not
authenticated. The server response was: 5.7.57 Client not
authenticated to send mail. Error: 535 5.7.3 Authentication
unsuccessful [DX0P273CA0007.AREP273.PROD.OUTLOOK.COM
2023-06-01T20:34:23.527Z 08DB62D998FCDD7E]

  • I have used direct password and did not work
  • Used App password and activating the MFA and did not work.

the below code is used for sending the email which I don’t think it has any issue

 SmtpClient smtpClient = new SmtpClient("smtp.office365.com", 587);
        smtpClient.EnableSsl = true;
        smtpClient.UseDefaultCredentials = false;
        smtpClient.Credentials = new NetworkCredential("[email protected]", "*******");

        // Set up the email message
        MailMessage mailMessage = new MailMessage();
        mailMessage.From = new MailAddress("[email protected]");
        mailMessage.To.Add("[email protected]");
        mailMessage.Subject = EmailSubject;
        mailMessage.Body = EmailMsg;
        mailMessage.IsBodyHtml = true;
        smtpClient.Send(mailMessage);

Application password is added as you can see
enter image description here

SMTP is enabled for that Mailbox also
enter image description here

SMTP Disabled status : not disabled
enter image description here
any help will be very apricated.
thanks

Tags:

2

Answers


  1. 0

    Sounds like 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 Enable or disable authenticated client SMTP submission (SMTP AUTH) in Exchange Online article.

    Login or Signup to reply.
  2. 0

    For smtp.office365.com to work, you need to do the following:

    1. Login into the Microsoft 365 Admin Center as an admin user.
    2. Click Azure Active Directory in the menu. If the option is not visible, click Show All. See image #1.
    3. In the Azure Active Directory, click Properties on the page. See Image #2
    4. At the bottom of the page, click Manage security defaults.
    5. Turn it off and answer why you are turing it off, the click Save. # See image #3
    6. Test your email code.

    Image #1
    enter image description here

    Image #2
    enter image description here

    enter image description here

    BTW, make sure you are using .NET Framework 4.8 ro later and user office365 MFA is disabled.

    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search