Add Gridview with tabled structure into the Textbox

i have my desired data in a grid.
i want to mail the contents of that grid in a tabled manner.
and the body of the mail is a textbox.

i have tried FreetextBox.
it works too..!!...but after sending the mail it shows in a HTML format to the client.!!

Dim str As StringBuilder = New StringBuilder()
Dim stringWriter As New StringWriter(str)
Dim _html As HtmlTextWriter = New HtmlTextWriter(stringWriter)
Dim ds As New DataSet()
ds = Session("CNF_Dataset_Mail")
Dim _gv As New GridView()
_gv = New GridView()
_gv.DataSource = Nothing
_gv.DataSource = ds
_gv.DataBind()
_gv.RenderControl(_html)