Yoan Blanc’s weblog

A friend of mine asked me : “How to get the default mail server of a company (with C#)”. He tried with nslookup but without any success. So I decided to try.

Some google searchs gives me the excellent tool called dig.

$ dig he-arc.ch MX
[...]
;; ANSWER SECTION:
he-arc.ch.              180     IN      MX      10 smtpgw1.he-arc.ch.
[...]

Using dig from C# isn’t really nice. It’s a big and ugly hack.

Another try with dnsJava. First step, convert the .jar into a library or executable for Mono via IKVM. It doesn’t work because of GNU Classpath isn’t fully complete and, probably, dnsJava uses too specific classes from the JRE/JDK of Sun.

Keep googling... And this article, the paradize on earth : C# .NET DNS query component. I downloaded the sources, removed the key.snk file, compiled the library and try this sample code :

using System;
using System.Net;
using Bdev.Net.Dns;

public class DnsTest {
   public static void Main(string[] argv) {
      // Shameful hardcoding of my DNS server (CableCom DNS server)
      IPAddress dnsServerAddress = IPAddress.Parse("62.2.17.60");
      
      // Retrieve the MX records for the domain dosimple.ch
      MXRecord[] records = Resolver.MXLookup("dosimple.ch", dnsServerAddress);
      
	   // iterate through all the records and display the output
      foreach (MXRecord record in records) {
          Console.WriteLine("{0}, preference {1}", record.DomainName, record.Preference);
      }
   }
}

It works. System.Net.Dns doesn’t need to specify the DNS server so, it’s a weird behaviour. There is a bug with these classes when a domain name contains a dash '-'.