SMTP Authentication with SmtpMail in .NET

Keywords: SMTP authentication SmtpMail MailMessage transport error 0x80040217

I recently had to send email from .NET code on a server that required SMTP authentication. It turns out the SmtpMail component does not expose any properties for specifying the user and password, but it does expose this ability through the Fields collection. There are various fields available in addition to those presented in this example, for instance those needed to authenticate with an Exchange server. The complete documentation is available here:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cdosys/html/_cdosys_schema_configuration.asp

Example:

MailMessage objMail = new MailMessage();
objMail.From = "user@mailserver.com";
objMail.To = "recipient@otherserver.com";
objMail.Subject = "test email";
objMail.Body = "test message";
objMail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", "user@mailserver.com");
objMail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", "password"); //this password must match the email password for user "user"
objMail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", 2);
SmtpMail.SmtpServer = "mailserver.com";
SmtpMail.Send(objMail);

On a side note, if the username or password is incorrect, the following cryptic error message is displayed:

The message could not be sent to the SMTP server. The transport error code was 0x80040217. The server response was not available.

Simply make sure the authentication information is correct. Also, make sure you specify the smtpauthenticate field with the correct value.

CAVEAT: The Fields property is only available in the .NET Framework 1.1 version of the MailMessage class. Make sure you are using 1.1.