You can't send a DataGridView to an email, any more than you could send a Button, and expect it to signal an event on your system when it was pressed. Suppose you could, and the remote system did not have .NET installed? What would happen then?
Instead, set the mail body to HTML (use MailMessage.IsBodyHtml = true), and send it as an HTML Table instead. This should help:
From DataGridView to HTML[
^]