List<string> aMyAttach = new List<string>();
  aMyAttach.Add("c:\\temp\\myfile.pdf") 
  //- Send the email with attachment.
  NetstairSMTPRelay.MailHelperV5 oMsg = new NetstairSMTPRelay.MailHelperV5();
  oMsg.BusinessInfo = "ABC, Inc";
  oMsg.SendAsyncEmail("johndoe@domain.com","", "Hello World", "Testing SMTP Relay", true, aMyAttach);
  var _sMailServerError = oMsg.Server_ErrorMessage;
  bool _bSuccessfullySent = oMsg.SuccessfullySent;            
  oMsg = null;

<system.net>
	<mailSettings>
		<smtp from="youremail@gmail.com">
		<network host="smtp.gmail.com" userName="youremail@gmail.com" password="{password goes here}" port="465" enableSsl="true" defaultCredentials="false" />
		</smtp>
	</mailSettings>
</system.net>