Try this code..
string Name="Mr Dev_Fady";
string Email = ur@email.com;
string textBody="Hi<strong>"+UserName+"</strong><br />"+Email+" BLAH BLAH BLAH"+
"<br > BLAH BLAH BLAH <table><tr><td>BLAH BLAH BLAH</td></tr></table>";
SmtpClient smtpClient = new SmtpClient();
MailMessage message = new MailMessage();
MailAddress fromAddress = new MailAddress(txt_From.Text);
smtpClient.Host = "localhost";
message.From = fromAddress;
message.To.Add(txt_To.Text);
message.Subject = txt_Subject.Text;
message.IsBodyHtml = true;
message.Body = textBody;
smtpClient.Send(message);