In Windows 2000, you'll find an implementation of nslookup. Type 'help' to get the full syntax of nslookup commands:

        > help
        Commands:   (identifiers are shown in uppercase, [] means optional)
        NAME            - print info about the host/domain NAME using default server
        NAME1 NAME2     - as above, but use NAME2 as server
        help or ?       - print info on common commands
        set OPTION      - set an option
            all                 - print options, current server and host
            [no]debug           - print debugging information
            [no]d2              - print exhaustive debugging information
            [no]defname         - append domain name to each query
            [no]recurse         - ask for recursive answer to query
            [no]search          - use domain search list
            [no]vc              - always use a virtual circuit
            domain=NAME         - set default domain name to NAME
            srchlist=N1[/N2/.../N6] - set domain to N1 and search list to N1,N2, etc.
            root=NAME           - set root server to NAME
            retry=X             - set number of retries to X
            timeout=X           - set initial time-out interval to X seconds
            type=X              - set query type (ex. A,ANY,CNAME,MX,NS,PTR,SOA,SRV)
            querytype=X         - same as type
            class=X             - set query class (ex. IN (Internet), ANY)
            [no]msxfr           - use MS fast zone transfer
            ixfrver=X           - current version to use in IXFR transfer request
        server NAME     - set default server to NAME, using current default server
        lserver NAME    - set default server to NAME, using initial server
        finger [USER]   - finger the optional NAME at the current default host
        root            - set current default server to the root
        ls [opt] DOMAIN [> FILE] - list addresses in DOMAIN (optional: output to FILE)
            -a          -  list canonical names and aliases
            -d          -  list all records
            -t TYPE     -  list records of the given type (e.g. A,CNAME,MX,NS,PTR etc.)
        view FILE           - sort an 'ls' output file and view it with pg
        exit            - exit the program
        >
        

There's a strong link between Internet email and the DNS. Mail servers use the DNS information database to route email messages from the originator to the recipient.

Basically, when the recipient email address is "someone@somewhere.com", the mail server searches the mail server (or Mail eXchanger) for domain "somewhere.com" in the DNS database. It then connects to the mail server (on port 25) and sends the email using SMTP.

Mail servers are registered in the DNS database as "Mail eXchanger" ("MX") records. Note that there can be several registered mail servers for a given domain (with a preference assigned to each server).

Using nslookup, you can find the email server of your domain, as shown in the sample session below.

Start a MS-DOS command prompt and type the nslookup command: C:\> nslookup Default Server: youserver.yourdomain Address: X.X.X.X > set type=MX > microsoft.com microsoft.com MX preference = 10, mail exchanger = mail1.microsoft.com microsoft.com MX preference = 20, mail exchanger = mail2.microsoft.com microsoft.com MX preference = 30, mail exchanger = mail3.microsoft.com microsoft.com MX preference = 40, mail exchanger = mail4.microsoft.com microsoft.com MX preference = 50, mail exchanger = mail5.microsoft.com

The lowest preference indicates the best (primary) mail server. A mailer would try it first and if it cannot connect to this server, it would use other servers (by order of preference).

You can test this "DNS Magic" by using the nslookup program shipped with Windows 2000, or with the DNS Magic HTML page. This component provides method ISimpleDNSClient::GetEmailServers() to find the registered email servers for a given domain.

For more about email and DNS, please see the reference documentation.

COMPONENT FEATURES

This component:

	implements the basics of DNS, as defined in RFC1034 and RFC1035,
	uses the resolver cache, queries first with UDP, then retries with TCP if the response is truncated
	asks the server to perform recursive resolution on behalf of the client to resolve the query
	finds DNS server addresses in local configuration (using API or Windows Registry)
	provides extended error information (ISupportErrorInfo and IErrorInfo are implemented)
	provides very small executable: 52 KB (MinSize) to 60 KB (MinDependency)
	requires no Graphical User Interface: the component can be used in non-GUI applications, like a Windows NT Service.
	is integrated with SimpleEmailClient (another component): the latter calls method GetEmailServers to automatically find SMTP servers
	runs on Windows 2000 (relies on Windows DNS API from the Platform SDK, August 2001)
	compiles with VC++ 6.0 SP5

USAGE

To use this component:

	create an instance of the component,
	(optionally) put/get properties from interface ISimpleDNSClient: ServerAddresses Separator
	call a method from interface ISimpleDNSClient: Resolve GetEmailServers GetDNSDomain FindPrimaryServer
	handle errors (try/catch in C++, On Error Resume Next in VBScript)

SAMPLE CODE (VBScript)

    Dim oDNS
    ' Create object instance
    Set oDNS = CreateObject("Emmanuel.SimpleDNSClient.1")

    ' Declare output variable 
    Dim found_names

    ' Set the server address(es)
    oDNS.ServerAddresses = "99.99.99.99"

    ' Set separator for output variable (if multiple results are found)
    oDNS.Separator = ", "

    ' (1) Find IP address of hostname "www.microsoft.com" (Internet class, type A)
    On Error Resume Next
    oDNS.Resolve "www.microsoft.com", found_names, "C_IN", "T_A"
    If Err <> 0 Then
        MsgBox Err.Description
    Else
        ' Show resolved names (within dialog box)
        MsgBox "Found names:" & vbCrLf & vbCrLf & found_names
    End If

    ' (2) Find Email Servers for domain "microsoft.com"
    On Error Resume Next
    oDNS.GetEmailServers "microsoft.com", found_names
    If Err <> 0 Then
        MsgBox Err.Description
    Else
        ' Show resolved names (within dialog box)
        MsgBox "Found names:" & vbCrLf & vbCrLf & found_names
    End If

Please refer to the test HTML files "TestSimpleDNSResolver.htm" and "TestDNSMagic.htm" for a full VBSsript example (see GUI below).

IMPLEMENTATION

	Base API is the new Windows 2000 DNS API This component relies on the Windows DNS API provided by the Windows Platform SDK (August 2001). The previous version was based on a porting of the BIND resolver library. Due to the high maintenance cost associated with this library, I decided to drop it when the DNS API came out. See the Component online documentation for more details.
	Automatic Conversion of reverse lookups (PTR) If your request is a reverse (IP address-> IP name) lookup (type PTR), then the component silently converts request to a in-arpa format. That is, if you request a resolution of type PTR for IP address "207.46.230.229", then the component will send a resolution request for "229.230.46.207.in-addr.arpa" (PTR). The result will be "www.international.microsoft.com".
	Find Email Server automatically The method GetEmailServers sends a request of type MX (Mail eXchanger) in order to find registered servers for a domain. It's only a shortcut for the Resolve method.
	Ignored Parameter: Resource Class Due to limitations in the current Windows DNS API, the parameter BResourceClass is ignored by the Resolve method (you should always use the default class "C_IN" for Internet Class).
	Ignored Property: ServerAddresses Due to limitations (bugs ?) in the current Windows DNS API, the property ServerAddresses is ignored by the Resolve method (the component always uses the local machine DNS configuration to find the DNS servers).

You can download the Microsoft Platform SDK from the Microsoft Web Site:
http://www.microsoft.com/msdownload/platformsdk/sdkupdate

TO DO LIST

	Test All DNS Resource Records (although all RR types are implemented, most of them couldn't be tested)
	Support DNS Security extensions (RFC 2535, "Domain Name System Security Extensions")

REFERENCE DOCUMENTATION

	Book: "DNS and BIND", by Paul Albitz & Cricket Liu, O'Reilly & Associates If you have to deal with DNS, I strongly recommend you to read this book: it's a very good presentation of DNS, from the protocol itself to the configuration tricks of a DNS server (using BIND). http://www.oreilly.com/catalog/dns3/index.html
	BIND (Berkeley Internet Name Domain), the reference implementation of the Domain Name System (DNS) protocols. http://www.isc.org/products/BIND
	A deprecated version of BIND, but who compiles and runs on Windows NT ftp://ftp.is.co.za/networking/ip/dns/bind/nt/kahn/ntbind497rel.zip
	RFC 1034: "DOMAIN NAMES - CONCEPTS AND FACILITIES" http://www.ietf.org/rfc/rfc1034.txt
	RFC 1035: "DOMAIN NAMES - IMPLEMENTATION AND SPECIFICATION" http://www.ietf.org/rfc/rfc1035.txt
	RFC 0974: "Mail routing and the domain system" http://www.ietf.org/rfc/rfc0974.txt
	RFC 1712: "DNS Encoding of Geographical Location" http://www.ietf.org/rfc/rfc1712.txt
	RFC 2181: "Clarifications to the DNS Specification" http://www.ietf.org/rfc/rfc2181.txt
	RFC 2671: "Extension Mechanisms for DNS (EDNS0)" http://www.ietf.org/rfc/rfc2671.txt
	RFC 2535: "Domain Name System Security Extensions" http://www.ietf.org/rfc/rfc2535.txt
	RFC 2536: "DSA KEYs and SIGs in the Domain Name System (DNS)" http://www.ietf.org/rfc/rfc2536.txt
	RFC 2538: "Storing Certificates in the Domain Name System (DNS)" http://www.ietf.org/rfc/rfc2538.txt
	Microsoft Plaform SDK - Domain Name System - "DNS Start Page" http://msdn.microsoft.com/library/en-us/dns/dnsstartpage_2lgl.asp
	Microsoft Plaform SDK - Domain Name System - "DNS Reference" http://msdn.microsoft.com/library/en-us/dns/dns_api_3fdx.asp
	Microsoft Plaform SDK - Domain Name System - "DNS Functions" http://msdn.microsoft.com/library/en-us/dns/dns_api_1wc3.asp
	Microsoft Plaform SDK - Domain Name System - "DNS Structures" http://msdn.microsoft.com/library/en-us/dns/dns_api_9837.asp
	Microsoft Plaform SDK - Download SDK http://www.microsoft.com/msdownload/platformsdk/sdkupdate

Download

Download FREE Binary (self-extracting kit) (191 KB).

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