.NET MVC contact form with dynamic/fillable "from" address

Question

I'm having issues coding my contact form in order to properly send e-mails with a "From" address that the user fills in. I get 5.7.1 responses informing me that the address doesn't belong to my account.

I know wordpress makes this possible however I'm not sure what the fault is on my C# project. I'm not sure if the sending host is supposed to be an e-mail account created on my domain for this purpose or should the credentials be from the machine I'm hosting on?

The project is depoyed to azure websites.

MailMessage mail = new MailMessage(cvm.FromMail, "[email protected]", cvm.Subject, sb.ToString());
          SmtpClient smtp = new SmtpClient();
          smtp.Host = "mydomain.host.com";
          smtp.Port = 587;
          smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
           smtp.UseDefaultCredentials = false;
          smtp.Credentials = new NetworkCredential("[email protected]", "*********");
          smtp.EnableSsl = true;
          smtp.Send(Mail);

I've tried many different combinations of port/ssl settings but still can't find success doing this.

Or should the host/credentials be something from my source azure website machine instead of my domain credentials?