Glossary · DNS
A DNS record's TTL is how many seconds resolvers may cache it before asking again, which sets how quickly changes take effect.
A TTL of 3600 means a resolver that has looked the record up can keep using that answer for up to an hour. Changes therefore appear gradually, as caches expire around the world.
Before a planned change, such as switching MX records during a migration, lower the TTL to around 300 seconds a day ahead, make the change, then raise it again once things are stable.
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