bird - 2:26 pm on Nov 2, 2002 (gmt 0)

The only issue I can think of is DNS caching. There may be a short time (roughly a week) after the switch where some e-mail (and web traffic) will still arrive at the old location, because some ISPs DNS servers haven't updated their records yet. Those updates will happen automatically, but since all DNS information has a certain "time to live" (TTL), that will not happen immediately.

If you have control about your old DNS entries, then you can take measures to shorten the cycle. Ideally, you would set the TTL of all your records to one day about two weeks before the switch. This means that conforming DNS servers will drop their cached records about that domain and request an update every 24 hours. There will be some that ignore the TTL information and still cache the records longer than specified, though. You can give the *new* DNS entries a TTL of about a week right away, which is a typical value chosen for efficiency reasons.

Ideally, you would then keep your website up at the old location for a week or two (or redirect it to the new IP), and it's also a good idea to forward any mail still arriving there for a while.

Note that there are seperate DNS records for web access (A = "address") and e-mail (MX = "mail exchange"). You need to make sure that both are configured correctly with your new DNS service. But since in most cases the DNS services are rendered by the hoster, that shouldn't be a problem.