Changing servers

[Steve <sjw@exegesis.org.uk>]

Hi,

I'm about to change a busy server (currently running under
RedHat) to a debian server. I'm trying to figure out a 
way that will cause least mail delays to our customers
whilst the dns records propagate (The IP's are going to
change for the mail server).

The current server runs sendmail and the replacement is
running postfix. What I would like to do at the changeover
is to get sendmail to automatically relay any incoming
mail over to the new machine based on it's IP and let
the new machine handle distribution. Is there an easy
way to do this with sendmail?

Also, I haven't come up with an easy solution for pop
mail.

I'd be grateful for any ideas and feedback.

--
Steve