Forms Data Controls :: Sending Mail To Multiple User Using Checkbox Within Gridview

I want to send mail tot multiple user using checkbox within gridbiew , but problem is it is sending mail to only first column email ID , and suppose i have four email id in databse then it will send 4 times mail to first email id,

OleDbCommand cmd = new OleDbCommand("select * from sendmail",con);
OleDbDataReader red = cmd.ExecuteReader();
if (red.Read())
{
StringBuilder str = new StringBuilder();
for (int i = 0; i < GridView1.Rows.Count; i++)
{
GridViewRow row = GridView1.Rows[i];
bool isChecked = ((CheckBox)row.FindControl("chkSelect")).Checked;
if (isChecked)
{
str.Append(GridView1.Rows[i].Cells[3].Text);
SmtpClient sc = new SmtpClient();
MailMessage mm = new MailMessage("dnk247@gmail.com", red["nemail"].ToString());
mm.Subject = "hello";
mm.Body = "just say hi";
sc.EnableSsl = true;
sc.Send(mm);
}
}
}