<asp:CreateUserWizard ID="userwizard" ContinueDestinationPageUrl="~/secretfiles/secret.aspx" runat="server" >
    <MailDefinition BodyFileName="register.txt" Subject="Registration Confirmation" From="[email protected]" />
    </asp:CreateUserWizard>

<mailSettings>
      <smtp deliveryMethod="Network" from="[email protected]">
        <network host="smtp.gmail.com" port="25" userName="[email protected]" password="sending emails's password" />
      </smtp>
    </mailSettings>

->Use localhost(SMTP)
->port=25
->authentication not required

<mailSettings>
  <smtp deliveryMethod="Network" from="[email protected]">
    <network enableSsl="true" host="smtp.gmail.com" port="25" userName="[email protected]" password="sending emails's password" />
  </smtp>
</mailSettings>

<mailSettings>
  <smtp deliveryMethod="Network" from="[email protected]">
    <network host="smtp.gmail.com" port="25" userName="[email protected]"
        password="sending emails's password" enableSsl="true" />
  </smtp>
</mailSettings>

protected void Button1_Click(object sender, EventArgs e)
{

    MailMessage mail = new MailMessage();
    MailAddress from = new MailAddress("your mail [email protected]");
    SmtpClient clientobj = new SmtpClient("smtp.gmail.com");
    mail.From = from;
    mail.To.Add(new MailAddress(" to mail [email protected]"));
    mail.Subject = "example gridview";
    mail.Body+="Please check below data <br/><br/>";
    mail.Body += getgridviewdata(gv1);
    mail.IsBodyHtml = true;
    clientobj.Credentials = new System.Net.NetworkCredential("your [email protected]", "your email password");
    clientobj.Port =587;
    clientobj.EnableSsl = true;
  clientobj.Send(mail);


}

public string getgridviewdata(GridView gv)
{
    StringBuilder strBuilder = new StringBuilder();
    StringWriter strWriter = new StringWriter(strBuilder);
    HtmlTextWriter htw = new HtmlTextWriter(strWriter);
    gv.RenderControl(htw);
    return strBuilder.ToString();
}
public override void VerifyRenderingInServerForm(Control control)
{
    /* Verifies that the control is rendered */
}

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="example.aspx.cs" Inherits="example" EnableEventValidation="false" %>