How to get the "Date" of an email?

I inspected the MailMessageObject and found this:

  Headers=HeaderCollection(5) 
  {
    "Uid",
    "DateCreated",
    "DateReceived",
    "Date",
    "IsRead"

So that means you have a total of three options available to you. The output will be in string format.

message.Headers["DateCreated"];
message.Headers["DateReceived"];
message.Headers["Date"];

You will want to look at the emails headers here is some documentation

http://msdn.microsoft.com/en-us/library/system.net.mail.mailmessage.headers.aspx

message.Headers["Date"];