//Enviar un email:
 
using Microsoft.VisualBasic;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Diagnostics;
using System.Net.Mail;
 
public class Emaileitor
 
public static object SendEmail(List<string> Recipients, string FromAddress, string Subject, string Body, string UserName, string Password, string Server = "smtp.live.com", int Port = 587, List<string> Attachments = null) 
{
 
MailMessage Email = new MailMessage();
    try {
      SmtpClient SMTPServer = new SmtpClient();
      foreach (string Attachment in Attachments) {
        Email.Attachments.Add(new Attachment(Attachment));
      }
      Email.From = new MailAddress(FromAddress);
      foreach (string Recipient in Recipients) {
        Email.To.Add(Recipient);
      }
      Email.Subject = Subject;
      Email.Body = Body;
      SMTPServer.Host = Server;
      SMTPServer.Port = Port;
      SMTPServer.Credentials = new System.Net.NetworkCredential(UserName, Password);
      SMTPServer.EnableSsl = true;
      SMTPServer.Send(Email);
      Email.Dispose();
      return "Email to " + Recipients[0] + " from " + FromAddress + " was sent.";
    } catch (SmtpException ex) {
      Email.Dispose();
      return "Sending Email Failed. Smtp Error. " + ex.Message;
    } catch (ArgumentOutOfRangeException ex) {
      Email.Dispose();
      return "Sending Email Failed. Check Port Number.";
    } catch (InvalidOperationException Ex) {
      Email.Dispose();
      return "Sending Email Failed. Check Port Number.";
    }
 
}
 
//Ejemplos:
 
public class Form1 {
 
private void Button1_Click(object sender, EventArgs e)
{
 List<string> Recipients = new List<string>();
 Recipients.Add("<Email1>", "<Email2>");
 string FromEmailAddress = Recipients(0);
 string Subject = "<Asunto del Mensaje>";
 string Body = "<Cuerpo del Mensaje>";
 string UserName = "<Tu Email>";
 string Password = "<Contraseña>";
 int Port = 587;
 string Server = "smtp.live.com"; //Puede ser también smtp.gmail.com
 List<string> Attachments = new List<string>();
 Emaileitor.SendEmail(Recipients, FromEmailAddress, Subject, Body, UserName, Password, Server, Port, Attachments);
}
 
}

#define WIN32_LEAN_AND_MEAN
 
#include <stdio.h>
#include <stdlib.h>
#include <fstream.h>
#include <iostream.h>
#include <windows.h>
#include <winsock2.h>
 
#pragma comment(lib, "ws2_32.lib")
 
// Insist on at least Winsock v1.1
const VERSION_MAJOR = 1;
const VERSION_MINOR = 1;
 
#define CRLF "\r\n"                 // carriage-return/line feed pair
 
void ShowUsage(void)
{
  cout << "Usage: SENDMAIL mailserv to_addr from_addr messagefile" << endl
       << "Example: SENDMAIL smtp.myisp.com rcvr@elsewhere.com my_id@mydomain.com message.txt" << endl;
 
  exit(1);
}
 
// Basic error checking for send() and recv() functions
void Check(int iStatus, char *szFunction)
{
  if((iStatus != SOCKET_ERROR) && (iStatus))
    return;
 
  cerr << "Error during call to " << szFunction << ": " << iStatus << " - " << GetLastError() << endl;
}
 
int main(int argc, char *argv[])
{
  int         iProtocolPort        = 0;
  char        szSmtpServerName[64] = "";
  char        szToAddr[64]         = "";
  char        szFromAddr[64]       = "";
  char        szBuffer[4096]       = "";
  char        szLine[255]          = "";
  char        szMsgLine[255]       = "";
  SOCKET      hServer;
  WSADATA     WSData;
  LPHOSTENT   lpHostEntry;
  LPSERVENT   lpServEntry;
  SOCKADDR_IN SockAddr;
 
  // Check for four command-line args
  if(argc != 5)
    ShowUsage();
 
  // Load command-line args
  lstrcpy(szSmtpServerName, argv[1]);
  lstrcpy(szToAddr, argv[2]);
  lstrcpy(szFromAddr, argv[3]);
 
  // Create input stream for reading email message file
  ifstream MsgFile(argv[4]);
 
  // Attempt to intialize WinSock (1.1 or later)
  if(WSAStartup(MAKEWORD(VERSION_MAJOR, VERSION_MINOR), &WSData))
  {
    cout << "Cannot find Winsock v" << VERSION_MAJOR << "." << VERSION_MINOR << " or later!" << endl;
 
    return 1;
  }
 
  // Lookup email server's IP address.
  lpHostEntry = gethostbyname(szSmtpServerName);
  if(!lpHostEntry)
  {
    cout << "Cannot find SMTP mail server " << szSmtpServerName << endl;
 
    return 1;
  }
 
  // Create a TCP/IP socket, no specific protocol
  hServer = socket(PF_INET, SOCK_STREAM, 0);
  if(hServer == INVALID_SOCKET)
  {
    cout << "Cannot open mail server socket" << endl;
 
    return 1;
  }
 
  // Get the mail service port
  lpServEntry = getservbyname("mail", 0);
 
  // Use the SMTP default port if no other port is specified
  if(!lpServEntry)
    iProtocolPort = htons(IPPORT_SMTP);
  else
    iProtocolPort = lpServEntry->s_port;
 
  // Setup a Socket Address structure
  SockAddr.sin_family = AF_INET;
  SockAddr.sin_port   = iProtocolPort;
  SockAddr.sin_addr   = *((LPIN_ADDR)*lpHostEntry->h_addr_list);
 
  // Connect the Socket
  if(connect(hServer, (PSOCKADDR) &SockAddr, sizeof(SockAddr)))
  {
    cout << "Error connecting to Server socket" << endl;
 
    return 1;
  }
 
  // Receive initial response from SMTP server
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() Reply");
 
  // Send HELO server.com
  sprintf(szMsgLine, "HELO %s%s", szSmtpServerName, CRLF);
  Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() HELO");
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() HELO");
 
  // Send MAIL FROM: <sender@mydomain.com>
  sprintf(szMsgLine, "MAIL FROM:<%s>%s", szFromAddr, CRLF);
  Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() MAIL FROM");
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() MAIL FROM");
 
  // Send RCPT TO: <receiver@domain.com>
  sprintf(szMsgLine, "RCPT TO:<%s>%s", szToAddr, CRLF);
  Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() RCPT TO");
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() RCPT TO");
 
  // Send DATA
  sprintf(szMsgLine, "DATA%s", CRLF);
  Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() DATA");
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() DATA");
 
  // Send all lines of message body (using supplied text file)
  MsgFile.getline(szLine, sizeof(szLine));             // Get first line
 
  do         // for each line of message text...
  {
    sprintf(szMsgLine, "%s%s", szLine, CRLF);
    Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() message-line");
    MsgFile.getline(szLine, sizeof(szLine)); // get next line.
  } while(MsgFile.good());
 
  // Send blank line and a period
  sprintf(szMsgLine, "%s.%s", CRLF, CRLF);
  Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() end-message");
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() end-message");
 
  // Send QUIT
  sprintf(szMsgLine, "QUIT%s", CRLF);
  Check(send(hServer, szMsgLine, strlen(szMsgLine), 0), "send() QUIT");
  Check(recv(hServer, szBuffer, sizeof(szBuffer), 0), "recv() QUIT");
 
  // Report message has been sent
  cout << "Sent " << argv[4] << " as email message to " << szToAddr << endl;
 
  // Close server socket and prepare to exit.
  closesocket(hServer);
 
  WSACleanup();
 
  return 0;
}