Question : Mail Flow:why would an MX lookup on a domain sporadically fail?

I have a weird DNS/Exchange Mail Problem
I have one domain that is a problem to me.   The domain is archwireless.net
I have the Internet connector set to  use DNS to send outbound mail over our internet connection via our ISA server.
From time to time, mail t one particular domain will queue and not be sent.  Issue seems to occur every couple of days.
When I switch the mail to flow OB via an offsite smart host service we sometimes use, mail is delivered to that domain.
Today, mail was again queuing to archwireless.net
I did a dnslookup for the MX record of archwireless.net and the query timed out.
I then did the same lookup for page.metrocall.com (a domain I know that uses the same MX record)
That query was successful.
I then queried archwireless.net again.  This time it returned the MX record.  The queue was then able to be cleared.
Mail will flow to archwireless.net for the next two, maybe three days but Im pretty sure it will eventually fail.
Does anyone know what I can do to fix this?
Other domains work fine.
If I send mail to this domain from elsewhere..like gmail, it works fine.

Its so sporadic I dont know what to think.  Doesnt seem to be an exchange issue at this point.  Doesnt seem to be ISA.    But I really dont know.
What should I I check first?
Any ideas would be great.

Exchange is 2003
DSN server is 2008
ISA is 2006

Answer : Mail Flow:why would an MX lookup on a domain sporadically fail?

Hi,
I took a look ang git this:

vs08:~#dig ns archwireless.net +short
ns1.archwireless.com.
ns3.mydyndns.org.
ns2.archwireless.com.
ns2.mydyndns.org.
ns5.mydyndns.org.
ns4.mydyndns.org.

So this domains has 6 nameservers.

But Querying MX for this domain only works on the archwireless nameservers, the mydns-servers do not reply:

vs08:~# dig mx archwireless.net +short @ns5.mydyndns.org
vs08:~# dig mx archwireless.net +short @ns2.archwireless.com
5 mailmx.usamobility.net.
vs08:~# dig mx archwireless.net +short @ns3.mydyndns.org
vs08:~# dig mx archwireless.net +short @ns2.mydyndns.org
vs08:~# dig mx archwireless.net +short @ns1.archwireless.com
5 mailmx.usamobility.net.
vs08:~# dig mx archwireless.net +short @ns4.mydyndns.org

Looks like archwireless has some issues on their nameservers, you cannot change that. You *could* create a special connector for this domain, but I would suggest having archwireless fix their problem.