[c#] 5.7.57 SMTP - Client was not authenticated to send anonymous mail during MAIL FROM error

I have to send mails using my web application. Given the below code showing The SMTP server requires a secure connection or the client was not authenticated. The server response was:

5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM.

Help me to find a proper solution. Thank you.

Code:

protected void btnsubmit_Click(object sender, EventArgs e)
 {

   Ticket_MailTableAdapters.tbl_TicketTableAdapter tc;
   tc = new Ticket_MailTableAdapters.tbl_TicketTableAdapter();
   DataTable dt = new DataTable();
   dt = tc.GetEmail(dpl_cate.SelectedValue);
   foreach (DataRow row in dt.Rows)
    {
    string eml = (row["Emp_Email"].ToString());
    var fromAddress = "emailAddress";
    var toAddress = eml;
    const string fromPassword = "*****";
    string body = "Welcome..";
 // smtp settings
    var smtp = new System.Net.Mail.SmtpClient();
       {
         smtp.Host = "smtp.office365.com";
         smtp.Port = 587;
         smtp.EnableSsl = true;

         smtp.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
         smtp.Credentials = new NetworkCredential(fromAddress, fromPassword);
         smtp.UseDefaultCredentials = false;
         smtp.Timeout = 600000;
       }
  // Passing values to smtp object
     smtp.Send(fromAddress, toAddress, subject, body);
     }
  } 
 }

I changed the Office365 password and then tried to send a test email and it worked like a charm for me.

I used the front end (database mail option) and settings as smtp.office365.com port number 587 and checked the secure connection option. use basic authentication and store the credentials. Hope this turns out useful for someone.

In my situation, our IT department made MFA mandatory for our domain. This means we can only use option 3 in this Microsoft article to send email. Option 3 involves setting up an SMTP relay using an Office365 Connector.

In my case I was using the MailMessage constructor that takes two strings (to, from) and getting the same error. When I used the default constructor and then added a MailAddress object to the To property of the MailMessage it worked fine.

I use to have the same problem.

Add the domain solved it..

mySmtpClient.Credentials = New System.Net.NetworkCredential("[email protected]", "password", "domain.com")

In my case, 2 Factor Authentication was turned on for the FROM account in Office 365. Once that was turned off, the email sent successfully.

This is an old question but since this is the first result in google for this error, I thought I would update my progress in this issue.

I spent way too may hours on this issue. In the end I had to change my Office 365 account's password few times until my code succeeded in sending emails.

Didn't have to make any changes in code.

Started working after adding property:

mail.smtp.starttls.enable=true

Using:

mail.smtp.host=smtp.office365.com
mail.smtp.port=587
mail.transport.protocol=smtp
mail.smtp.auth=true
mail.smtp.starttls.enable=true
[email protected]
mail.smtp.password=xxx
[email protected]

Probably the password of the account that you trying to send e-mail is expired. Just check your password policy expire date.

If you are using office 365 follow this steps:

1. check the password expiration time using Azure power shell :Get-MsolUser -All | select DisplayName, LastPasswordChangeTimeStamp
2. Change the password using a new password (not the old one). You can eventually go back to the old password but you need to change it twice.

Hope it helps!

Try resetting your password for the email used. Had similar issue, and got it fixed only after changing password.

I spent way too much time on this and the solution was super simple. I had to use my "MX" as the host and port 25.

        var sClient = new SmtpClient("domain-com.mail.protection.outlook.com");
        var message = new MailMessage();

        sClient.Port = 25;
        sClient.EnableSsl = true;
        sClient.Credentials = new NetworkCredential("user", "password");
        sClient.UseDefaultCredentials = false;

        message.Body = "Test";
        message.From = new MailAddress("[email protected]");
        message.Subject = "Test";
        message.CC.Add(new MailAddress("[email protected]"));

        sClient.Send(message);

Main two reasons only as mentioned in above comments

1. NetworkCredentials you set should be correct. Verify with try actually signing into the account.
2. You need to set UseDefaultCredentials to false first and then set Credentials Or Put smtp.UseDefaultCredentials = false; above the smtp.Credentials assignment.

If you reorder your code this way, it should work:

SmtpClient client = new SmtpClient();
client.UseDefaultCredentials = false;
client.Credentials = new System.Net.NetworkCredential(mailOut, pswMailOut);
client.Port = 587; // 25 587
client.Host = "smtp.office365.com";
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.EnableSsl = true;

MailMessage mail = new MailMessage();            
mail.From = new MailAddress(mailOut, displayNameMailOut);
mail.To.Add(new MailAddress(mailOfTestDestine));
mail.Subject = "A special subject";
mail.Body = sb.ToString();

client.Send(mail);

@Reshma- In case you have not figured it yet, here are below things that I tried and it solved the same issue.

1. Make sure that NetworkCredentials you set are correct. For example in my case since it was office SMTP, user id had to be used in the NetworkCredential along with domain name and not actual email id.

2. You need to set "UseDefaultCredentials" to false first and then set Credentials. If you set "UseDefaultCredentials" after that it resets the NetworkCredential to null.

Hope it helps.

Set the User default credentials to true:

 smtp.UseDefaultCredentials = True;

Before that, input your credential:

smtp.Credentials = new NetworkCredential(fromAddress, fromPassword);

This should work fine.