Enviar correo usando DNS

A veces, enviar correos electrónicos utilizando un servidor SMTP no es factible para los requisitos de un proyecto. Puede que queramos utilizar el registro MX del nombre de dominio del destinatario. El siguiente fragmento de código muestra cómo enviar correos electrónicos utilizando los servidores de correo del dominio del destinatario.

// For complete examples and data files, please go to https://github.com/aspose-email/Aspose.Email-for-.NET

static void Main(string[] args)
{
	try
	{
		MailMessage msg = new MailMessage("[e-mail]", "[e-mail]", "test", "this is a test");
		msg.CC.Add(new MailAddress("[e-mail]", "CC Display Name"));
		DnsSendMessage(msg);
	}
	catch (Exception e)
	{
		Console.WriteLine(e.Message);
	}
}

private static void DnsSendMessage(MailMessage msg)
{
	// Get all the recipients in to, cc and bcc in one collection
	MailAddressCollection addresses = new MailAddressCollection();
	foreach (MailAddress to in msg.To)
	{
		addresses.Add(to);
	}

	foreach (MailAddress cc in msg.CC)
	{
		addresses.Add(cc);
	}
		
	foreach (MailAddress bcc in msg.Bcc)
	{
		addresses.Add(bcc);
	}
		
	// Send mail using DNS to each address
	foreach (MailAddress addr in addresses)
	{
		// Find mail exchange servers with the help of DnsClient
		DnsClient dnsClient = new DnsClient();
		Question mxQuestion = new Question(addr.Host, QueryType.MX);
		if (dnsClient.Resolve(mxQuestion))
		{
			// Try to send a message
			foreach (ResourceRecord record in dnsClient.ReceivedMessage.Answers)
			{
				MXResourceRecord cnRecord = record as MXResourceRecord;
				if (cnRecord != null)
				{
					try
					{
						// Send message
						SmtpClient client = new SmtpClient();
						client.AuthenticationMethod = SmtpAuthentication.None;
						client.Host = cnRecord.ExchangeName;
						client.Port = 25;
						client.Send(msg);
						Console.WriteLine("Mail sent to " + addr.Address);
					}
					catch (SmtpException e)
					{
						Console.WriteLine(cnRecord.ExchangeName + ": " + e.Message + Environment.NewLine);
						continue;
					}
				}
			}
		}
	}
}