How to write contents as CDATA in XML using c#?

You can add the CDATA section using the XmlDocument's CreateCDataSection
method. See the below example in C#:
XmlDocument doc = new XmlDocument();
doc.LoadXml( docContent );
XmlNode cdataParent = doc.SelectSingleNode( "path to the node where you want
to add the email text" );
cdataParent.AppendChild( doc.CreateCDataSection( cdataContent ) );