How to change a record without downtime (lower the TTL first)

When you're about to move a site or mail to a new server, a bit of planning avoids an outage:

1. A day before the change, edit the record you'll be moving and drop its TTL to 300s (5 minutes). Save.
2. Wait for the old, longer TTL to expire everywhere — i.e. wait at least as long as the previous TTL. Now resolvers are only caching the record for 5 minutes.
3. Make the real change (point the A record at the new IP, swap the MX, etc.).
4. Because the TTL is now short, the change propagates within minutes rather than hours.
5. Once you've confirmed everything works on the new target, raise the TTL back to 3600s to reduce lookup load.

This technique turns a nerve-wracking migration into a near-instant cutover, and it's the single most useful DNS habit to adopt.