Yes you can send mail through gmail to the client if the SMTP server is not installed.
string emailid=emailtxt.Text;
MailMessage mail = new MailMessage();
mail.To.Add(emailid);
mail.From = new MailAddress("xyz@gmail.com");
mail.Subject = "Email using Gmail";
string Body = "Hi all" ;
mail.Body = Body;
mail.IsBodyHtml = true;
SmtpClient smtp = new SmtpClient();
smtp.Host = "smtp.gmail.com";
smtp.Credentials = new System.Net.NetworkCredential
("xyz@gmail.com", "yourpassword");
smtp.EnableSsl = true;
smtp.Send(mail);
yourpassword here is the gmail password.