Send email works in Editor, not on tablet

This is my code :

 void Mail(){
         MailMessage mail = new MailMessage();
         mail.From = new MailAddress("aaaaa@gmail.com");

         mail.To.Add("bbbb@.com.vn");
         mail.Subject = "Hello!!!";
         mail.Body = "This is word and image for you.";
         string attachmentPath = filename;
         Debug.Log(attachmentPath);
         Attachment attachmentFile = new Attachment(attachmentPath);
         mail.Attachments.Add(attachmentFile);
         SmtpClient smtpServer = new SmtpClient("smtp.gmail.com");
         smtpServer.Port = 587;
         #if UNITY_IPHONE
         smtpServer.Credentials = new System.Net.NetworkCredential("aaaaaaaa@gmail.com", "xxxxxxxxx") as ICredentialsByHost;
         
         #endif
         #if UNITY_EDITOR_WIN
         smtpServer.Credentials = new System.Net.NetworkCredential("aaaaaaaa@gmail.com", "xxxxxxxxx") as ICredentialsByHost;
         #endif
         smtpServer.EnableSsl = true;
         ServicePointManager.ServerCertificateValidationCallback = 
             delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) 
         { return true; };
         smtpServer.Send(mail);
     }

• I run on unity3d ==> it is good.

• I build into ios,android ==> install on device ==> run ==> it is error ( i don't see email )

• Why?? and Why??.