Why header fields are converted to lower case when usingMailMessage.Headers.Add(...)?

[Afshar]

Hi all,

After running following code, "My-Header" turns to "my-header" in
email received by destination. I want it to be sent just like "My-
Header". I don't love any case convert no "upper" nor "lower".

MailMessage mail = new MailMessage("so*****@gmail.com",
"so*****@gmail.com", "test", "Hello");
mail.Headers.Add("My-Header", "123");
SmtpClient client = new SmtpClient();
client.EnableSsl = true;
client.Send(mail);

Thanks in Advance