how to assign MX record to the domain

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C#

ASP.NET

I am sending xml via a webrequest, and if the webrequest is successful, it creates an email.
however, I am currently getting a error, from the web response, such as- "The domain reply.domain.com doesn't have a valid MX record"

How can I setup up mx record for my email address?

pubic static string xml()
{
XElement xeRoot = new XElement("mail_job");

XElement xeStatus = new XElement("subject", "Draft");
xeRoot.Add(xeStatus);

XElement xeDisplayDate = new XElement("from_name", "####");
xeRoot.Add(xeDisplayDate);

XElement xeDisplayTitle = new XElement("from_address", "info@reply.domain.com");
xeRoot.Add(xeDisplayTitle);

XElement xeTemplate = new XElement("reply_address", "info@reply.domian.com");
xeRoot.Add(xeTemplate);
}


 public static string WRequest()
{
string URL = Response.createEmailURL();
string method = "POST";
string postData = xml();

string responseData = "";
int statusCode;
//rest of the code

}

Any hints would be most helpful?
Thank you