System.Net.Mime.HeaderCollection class

When I retrieve email.Headers.ToString, I get System.Net.Mime.HeaderCollection. I have been searching on google for quite some time but I am unable to find any information about the class. Is there any website in which I can research more into the class as mentioned above? I am trying to retrieve the full header of an email.

System.Net.Mime Namespace has only following class.
For HeaderCollection class check below post.