MX question

[Alan J Rosenthal]

dsantera at my-deja.com writes:
>There are
>approx. 80 customers using this server and each one has an A rec and MX
>rec pointing to the server.  When I move the server I am also going to
>be changing the IP address of the box.  Any suggestions on how to have
>the old address redirect the user to the new server?

Leave a machine running on the old address (presumably in the old location)
running an MTA configured to be willing to relay to that list of 80 domains,
and make sure that that machine has the up-to-date information (restart
a local name server or whatever it takes to clear out the old info).
Then callers using the old address will send the mail successfully to the
old address, and it will then be retransmitted to the new machine.

But this oughtn't be necessary.  Before the move, drop your TTL down to the
amount of time left until the move, or a minimum of about 30 minutes as the
move is imminent.  Then move and put the TTL back up.  There will be a window
of something around 30 minutes where clients can get the old address even
though you've already moved; all MTAs will queue and try again and then
they'll get the new address eventually, no mail lost.