Email attachment on Android & iOS

Hi! I'm trying to send an email using google server with this code:

 MailMessage mail = new MailMessage();
         
         mail.From = new MailAddress("MAILFROM");
         mail.To.Add("MAILTO");
         mail.Subject = "Test Mail Subject";
         mail.Body = "Test Mail Body";
 
         SmtpClient smtpServer = new SmtpClient("smtp.gmail.com");
         smtpServer.Port = 587;
         smtpServer.Credentials = new System.Net.NetworkCredential ("LOGIN", "PASSWORD");
         smtpServer.EnableSsl = true;
         ServicePointManager.ServerCertificateValidationCallback = 
             delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) {
             return true;
             };
         try {
             smtpServer.Send(mail);
             } catch (Exception e) {
                 Debug.Log (e.GetBaseException ());
             }

and it works.

Now I would add an attachment that is in StreamingAssets folder; I tryed in dozens of ways, like

 System.Net.Mail.Attachment attachment;
 attachment = new System.Net.Mail.Attachment (string.Format (@"Assets/StreamingAssets/{0}", "FILENAME"));
 mail.Attachments.Add(attachment);

but... NOTHING, no email sent.

Some idea?

Thank you!

EDIT:

Solved this way:

 string FilePath = "";
 string AttachmentName = "ATTACHNAME";
 string FileName = "";
 
 #if UNITY_EDITOR
             FilePath = string.Format(@"Assets/StreamingAssets/{0}", AttachmentName);
         #else
             FilePath = Application.persistentDataPath + "/" + AttachmentName;
             if(!File.Exists(FilePath)) {
                 WWW loadImage = new WWW("jar:file://" + Application.dataPath + "!/assets/" + AttachmentName);
                 while(!loadImage.isDone) {}
                 File.WriteAllBytes(FilePath, loadImage.bytes);
             }
         #endif
         
         FileName = FilePath;
 
         MailMessage mail = new MailMessage();
         
         mail.From = new MailAddress("FROMEMAIL");
         mail.To.Add("TOEMAIL");
         mail.Subject = "eMail Subject";
         mail.Body = "eMail Body";
 
         Attachment data = new Attachment(FileName, System.Net.Mime.MediaTypeNames.Application.Octet);
             // Add time stamp information for the file.
             System.Net.Mime.ContentDisposition disposition = data.ContentDisposition;
             disposition.CreationDate = System.IO.File.GetCreationTime(FileName);
             disposition.ModificationDate = System.IO.File.GetLastWriteTime(FileName);
             disposition.ReadDate = System.IO.File.GetLastAccessTime(FileName);
 
         mail.Attachments.Add(data);
 
         SmtpClient smtpServer = new SmtpClient("smtp.gmail.com");
         smtpServer.Port = 587;
         smtpServer.Credentials = new System.Net.NetworkCredential ("LOGIN", "PASSWORD");
         smtpServer.EnableSsl = true;
         ServicePointManager.ServerCertificateValidationCallback = 
             delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) {
             return true;
             };
         try {
             smtpServer.Send(mail);
             } catch (Exception e) {
                 Debug.Log (e.GetBaseException ());
             }