これを使用してメールを送信すると、使用した本文の文字列が壊れません
NetworkCredential loginInfo = new NetworkCredential("bhavik778@gmail.com", mypassword);
MailMessage msg = new MailMessage();
msg.From = new MailAddress("bhavik778@gmail.com");
msg.To.Add(new MailAddress(tomyclient));
msg.Subject = "Message from CLB Website.";
msg.Body = "Following message was sent to you :-<br/>" + name + "<br/>" + email_id + "<br/>" + Query;
msg.IsBodyHtml = true;
SmtpClient client = new SmtpClient("smtp.gmail.com", 587);
client.EnableSsl = false;
client.UseDefaultCredentials = false;
client.Credentials = loginInfo;
client.Send(msg);