try 
              { 
                  SmtpClient istemci = new SmtpClient("mail.domainadi.com"); 
                  MailAddress gon = new MailAddress("info@domainadi.com"); 
                  MailAddress alici = new MailAddress(mailadresi.Text); 
                  MailMessage mail = new MailMessage(gon, alici); 
                  mail.Subject = "mesajjj"; 
                  mail.Body = "mesajj"; 
                  istemci.Send(mail); 
              } 
              catch (Exception ex) 
              { 
                  lblmsg.Text = ex.Message; 
              }