Moving a server and updating tables

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Hey everyone,

The time has come to where we have grown beyond serving on one box. Up
until this point, I've run a primary and secondary DNS, along with
Webstar 4.4 on two servers. One server took the brunt of our load,
running http, ftp and pop for several years. With massive increases in
mail traffic over the past 12 months, it's really grown beyond time to
separate off at least the mail services to the second machine. We did
such over the weekend, adding in all of the existing accounts from the
primary server (we'll call .5) to the other server (.6)

Webstar's mail has a bonus feature of supporting webmail, so during the
transition from one box to the other, any straggler messages that came
to .5 could be picked up via browser if the DNS for that individual's
ISP had already updated and was directing POP requests to the new
server (all old accounts on .5 have been left active). To make sure we
didn't bounce anything, we set up MX records like so:

mydomain.com MX 10 new.mail.server
mydomain.com MX 20 old.mail.server

After all entries were completed, both of our DNS servers were
restarted.

Updating the DNS was simple enough, and for most of my customers, the
transition went without a hitch.

However, for two domains, and one email account on one domain, after
nearly 60 hours, their POP clients continue to be pointed to the old
server. Their mail is being successfully collected on the new server.
Both of the domains in question are served by two separate DSL carriers
in North Carolina -- so I'm hoping their DNS systems are simply kind of
slothish. However, the oddity is that the one email account POP client
from one of our domains continues to go to the old server (it is a list
serve POP account) while all other POP accounts for the same domain --
and all email from the outside, is properly routed to the new mail
server. Very weird, as that list server lives under our roof, and has
other list accounts which check the new server without issue for the
same domain!

Anyone have any ideas? Would I be better off removing the second MX
record from each zone for a while and somehow forcing the clients to
relookup to the new server on recalcitrant individual accounts or
zones? (Boy, I hate the thought of re-entering them.

A second question: if I want to run the old server as a backup mail
server, but don't want it to see any traffic to speak of unless the
primary mail server goes down, what are the recommended MX priority
settings? I've currently set the MX records as stated above, but don't
know the benefit of raising the value to 100, or 1000, or whatever. I
tried 65000 for one zone, but my version of QDNS 3.0.1 gave funky
errors (a negative number in the record) until I dropped it back down
to 1000 on that test. Is this value like the load balancing numbers,
where it is a ratio of hits rather than a fall-over order?

Thanks for the remedial education.

paul

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