[Exim] HI. Swapping mail servers.

I am about to swap in a new mail server, so I can rebuild the current one.
I'm wondering if I can get some suggestions how to do this with minimal
downtime.. One thing I thought of was setting the current box (#1) to
queue_only and have no queue running for a bit, then move in the new box
(#2) with the IP of #1, and set #2 to queue_only and then on #1 is FTP
over my /var/mail/ directory to #2, then somehow (suggestions on this
please - would I do a smarthost on #1?) send all the mail in queue from #1
to #2, and then set #2 to deliver normally.

Make sense? Sound like a reasonable way to do this?