Finding MX Records

[Kevin Darcy]

You don't have to have an MX record to receive mail. Read RFC 974; if there's
no MX record, look for an A record and deliver to that instead.

What you're seeing in the "nslookup" output is an SOA record being returned in
the Authority section of the nameserver's response; a perfectly valid response
when there is no data which matches the query (see RFC 2308 for details).


- Kevin

Matthew Thompson wrote:

> I've come across something that to an extent has stumped me.
>
> I've written a DNS query client in VB (Please no comments about the choice
> of language) which takes an email address and attempts to determine wether
> the destination is deliverable. IT performs an query to our local DNS server
> and then it either returns a positive (if it receives MX entries) or queries
> the NS records it receives back.
>
> This looks to have worked pretty well so far but a small number of the
> failed addresses would appear to have no MX records associated.
>
> One example is thmc.com.tw
>
> My software queries our local DNS server and gets back the following (as
> nslookup displays it)
>
> Server:  [10.1.1.245]
> Address:  10.1.1.245
>
> thmc.com.tw
>         origin = thmcsrv.thmc.com.tw
>         mail addr = administrator.thmc.com.tw
>         serial = 24
>         refresh = 3600 (1 hour)
>         retry   = 600 (10 mins)
>         expire  = 86400 (1 day)
>         minimum ttl = 3600 (1 hour)
>
> 10.1.1.245 is the internal nic on the DNS server - it is connected to the
> Internet properly.
>
> If I perform the query on thmcsrv.thmc.com.tw I get _exactly_ the same back
> from that server as well.
>
> So I'm leaft wondering 1. are the addresses valid and 2 how do I know if
> they are.
>
> Any assistance greatly appreciated.
>
> M at t :o)
>
> --
> Matthew Thompson - Fairplay Publications Limited - www.fairplay.co.uk
> matthewt at fairplay.co.uk - tel: +44 20 8645 2800 - fax: +44 20 8660 2824
> 20 Ullswater Crescent, Coulsdon Surrey CR5  2HR  United Kingdom
> Registered in England No. 338580