On Thu, 15 Jun 20:59:59, "Blaine E. Thompson" <[log in to unmask]> wrote:
> I have a subscriber to my list, Grunge-L (Ubvm.cc.buffalo.edu) who is
> subscribed from Net4LS.boat.bt.com.  Every day or two, I begin to get error
> messages claiming that the site is unknown. Yet, this subscriber posts to the
> list, etc. We're now on 1.8b (I think...) so, he gets automatically deleted
> too. He posts to our list frequently, and is a "good" subscriber, in that he
> does not violate etiquette, etc... I did a nslookup, and it returned no
> Address (A) records for the site. Any ideas?
 
You should have asked NSLOOKUP for the NS (NameServer) and MX (Mail Exchanger)
records.  If you did, you would have found two NS records:
 
   bt.com  nameserver =  zaphod.axion.bt.co.uk
   bt.com  nameserver = leopard.axion.bt.co.uk
 
If you ask 'ZAPHOD', it returns two MX records:
 
   > server  zaphod.axion.bt.co.uk.
   > net4ls.boat.bt.com
   Server:  zaphod.axion.bt.co.uk
   Address:  132.146.5.1
 
   net4ls.boat.bt.com   preference = 10, mail exchanger = zaphod.axion.bt.co.uk
   net4ls.boat.bt.com   preference = 20, mail exchanger = relay.bt.net
 
If you ask 'LEOPARD', it returns the message:
 
   > server leopard.axion.bt.co.uk.
   > net4ls.boat.bt.com
   Default Server:  leopard.axion.bt.co.uk
   Address:  132.146.137.1
   *** No mail exchanger (MX) records available for net4ls.boat.bt.com
 
Obviously, depending on which NameServer is (randomly) asked,
E-mail to your subscriber will (randomly) either get delivered or bounced.
 
Since LISTSERV doesn't actually deliver the posting,
i.e., it relies on some SMTP-server to find and use the MX-records,
this is not a "LISTSERV-problem".
 
I've sent a copy of this message to the "start-of-authority" person
for the 'BT.CO.UK' domain.  He/she is the only person who can get this
'LEOPARD' to change its spots.  :-),