migration of mail server

[mok swee loong]

hi all!

apology for this is not exactly a qmail specified question - we do use qmail
though. ;)
we are on the process of migrating of mail server, now have come to the
point that we need to change

mail.mydomain.com from 123.123.123.123 (old server ip) to 345.345.345.345
(new server ip)

wonder if anyone have any advice or experience on how to go about this
process? what are the better way to do this, in order to minimize /
eliminate the chances of lost mail?

thanks in advance!!

best regards,
mok