> I've been dealing with our sys admins and zmailer gurus and I have found out
> that Zmailer develops fantastic queues.  The DNS spends a lot
> of time resolving
> addresses and by virtue of that all mail is delayed while it
> waits for the DNS
> times out and gives up on each bad look up.
 
Sounds like you need to upgrade your DNS machine (or offload some
of the work somehow). IF it's really taking that long to resolve
addresses, there's somethig very wrong.
 
>Altogether we have 80+ lists at the moment.  So periodilcally, the DNS can get
> flooded with a massive amount of look up requests.
> As far as I can determine the backlog lies within the router of Zmailer.
> Everything sits around waiting for the overworked DNS.
 
Couple suggestions:
 
1) setup a cache-only name server on the LISTSERV machine. This
will vastly reduce the number of queries your primary DNS has to
deal with (in fact, this is a good idea for any machine with
heavy mail traffic).
 
2) Look into using sendmail 8.7.5 in place of Zmailer. sendmail
8.7 is still slower than LSMTP, but it's a vast improvement over
sendmail 5.x, which Zmailer was intended to replace.
 
3) Look into LSMTP to offload the mail delivery processing.