Creo que ustedes no pueden tener acceso para bajar el file,
lo voy a checar, pero mientras aqui les dejo el code completo (copy and paste)
Código PHP:
using System;
using System.Text;
using System.IO;
using System.Net.Sockets;
using System.Net;
using System.Web.Mail;
namespace SMTP
{
/// <summary>
/// provides methods to send email via smtp direct to mail server
/// </summary>
public class SmtpDirect
{
/// <summary>
/// Get / Set the name of the SMTP mail server
/// </summary>
public static string SmtpServer;
private enum SMTPResponse: int
{
CONNECT_SUCCESS = 220,
GENERIC_SUCCESS = 250,
DATA_SUCCESS = 354,
QUIT_SUCCESS = 221
}
public static bool Send(MailMessage message)
{
IPHostEntry IPhst = Dns.Resolve(SmtpServer);
IPEndPoint endPt = new IPEndPoint(IPhst.AddressList[0], 25);
Socket s = new Socket(endPt.AddressFamily, SocketType.Stream,ProtocolType.Tcp);
s.Connect(endPt);
if(!Check_Response(s, SMTPResponse.CONNECT_SUCCESS))
{
s.Close();
return false;
}
Senddata(s, string.Format("HELO {0}\r\n", Dns.GetHostName() ));
if(!Check_Response(s, SMTPResponse.GENERIC_SUCCESS))
{
s.Close();
return false;
}
Senddata(s, string.Format("MAIL From: {0}\r\n", message.From ));
if(!Check_Response(s, SMTPResponse.GENERIC_SUCCESS))
{
s.Close();
return false;
}
string _To = message.To;
string[] Tos= _To.Split(new char[] {';'});
foreach (string To in Tos)
{
Senddata(s, string.Format("RCPT TO: {0}\r\n", To));
if(!Check_Response(s, SMTPResponse.GENERIC_SUCCESS))
{
s.Close();
return false;
}
}
if(message.Cc!=null)
{
Tos= message.Cc.Split(new char[] {';'});
foreach (string To in Tos)
{
Senddata(s, string.Format("RCPT TO: {0}\r\n", To));
if(!Check_Response(s, SMTPResponse.GENERIC_SUCCESS))
{
s.Close();
return false;
}
}
}
StringBuilder Header=new StringBuilder();
Header.Append("From: " + message.From + "\r\n");
Tos= message.To.Split(new char[] {';'});
Header.Append("To: ");
for( int i=0; i< Tos.Length; i++)
{
Header.Append( i > 0 ? "," : "" );
Header.Append(Tos[i]);
}
Header.Append("\r\n");
if(message.Cc!=null)
{
Tos= message.Cc.Split(new char[] {';'});
Header.Append("Cc: ");
for( int i=0; i< Tos.Length; i++)
{
Header.Append( i > 0 ? "," : "" );
Header.Append(Tos[i]);
}
Header.Append("\r\n");
}
Header.Append( "Date: " );
Header.Append(DateTime.Now.ToString("ddd, d M y H:m:s z" ));
Header.Append("\r\n");
Header.Append("Subject: " + message.Subject+ "\r\n");
Header.Append( "X-Mailer: SMTPDirect v1\r\n" );
string MsgBody = message.Body;
if(!MsgBody.EndsWith("\r\n"))
MsgBody+="\r\n";
if(message.Attachments.Count>0)
{
Header.Append( "MIME-Version: 1.0\r\n" );
Header.Append( "Content-Type: multipart/mixed; boundary=unique-boundary-1\r\n" );
Header.Append("\r\n");
Header.Append( "This is a multi-part message in MIME format.\r\n" );
StringBuilder sb = new StringBuilder();
sb.Append("--unique-boundary-1\r\n");
sb.Append("Content-Type: text/plain\r\n");
sb.Append("Content-Transfer-Encoding: 7Bit\r\n");
sb.Append("\r\n");
sb.Append(MsgBody + "\r\n");
sb.Append("\r\n");
foreach(object o in message.Attachments)
{
MailAttachment a = o as MailAttachment;
byte[] binaryData;
if(a!=null)
{
FileInfo f = new FileInfo(a.Filename);
sb.Append("--unique-boundary-1\r\n");
sb.Append("Content-Type: application/octet-stream; file=" + f.Name + "\r\n");
sb.Append("Content-Transfer-Encoding: base64\r\n");
sb.Append("Content-Disposition: attachment; filename=" + f.Name + "\r\n");
sb.Append("\r\n");
FileStream fs = f.OpenRead();
binaryData = new Byte[fs.Length];
long bytesRead = fs.Read(binaryData, 0, (int)fs.Length);
fs.Close();
string base64String = System.Convert.ToBase64String(binaryData, 0,binaryData.Length);
for(int i=0; i< base64String.Length ; )
{
int nextchunk=100;
if(base64String.Length - (i + nextchunk ) <0)
nextchunk = base64String.Length -i;
sb.Append(base64String.Substring(i, nextchunk));
sb.Append("\r\n");
i+=nextchunk;
}
sb.Append("\r\n");
}
}
MsgBody=sb.ToString();
}
Senddata(s, ("DATA\r\n"));
if(!Check_Response(s, SMTPResponse.DATA_SUCCESS))
{
s.Close();
return false;
}
Header.Append( "\r\n" );
Header.Append( MsgBody );
Header.Append( ".\r\n" );
Header.Append( "\r\n" );
Header.Append( "\r\n" );
Senddata(s, Header.ToString());
if(!Check_Response(s, SMTPResponse.GENERIC_SUCCESS ))
{
s.Close();
return false;
}
Senddata(s, "QUIT\r\n");
Check_Response(s, SMTPResponse.QUIT_SUCCESS );
s.Close();
return true;
}
private static void Senddata(Socket s, string msg)
{
byte[] _msg = Encoding.ASCII.GetBytes(msg);
s.Send(_msg , 0, _msg .Length, SocketFlags.None);
}
private static bool Check_Response(Socket s, SMTPResponse response_expected )
{
string sResponse;
int response;
byte[] bytes = new byte[1024];
while (s.Available==0)
{
System.Threading.Thread.Sleep(100);
}
s.Receive(bytes, 0, s.Available, SocketFlags.None);
sResponse = Encoding.ASCII.GetString(bytes);
response = Convert.ToInt32(sResponse.Substring(0,3));
if(response != (int)response_expected)
return false;
return true;
}
}
}
donde viene la clase SmtpDirect 
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