Correct TTL value for domain MX record

What is the correct Time to Live (TTL) value that an email domain's MX record should be set to?
IT GuyNetwork EngineerAsked:
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Dan Dhillon2nd/3rd line Support EngineerCommented:
Hi knowledgeable,

Should be 60 mins.
IT GuyNetwork EngineerAuthor Commented:
Is 60 minutes the recommended setting for an Office 365 domain?

What happens if it is set higher?

The organization I am currently working for has it set to 24 hours. Will that present a problem or a security risk?
Dan Dhillon2nd/3rd line Support EngineerCommented:
In you office 365 admin centre you can run the domain verification tool which will tell you what ttl to use for mx records.
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IT GuyNetwork EngineerAuthor Commented:
The organization I am currently working for has their email domain MX record set to 24 hours. Will that present a problem or a security risk?
Dan Dhillon2nd/3rd line Support EngineerCommented:

Hope this helps answers your question.

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DP230Network AdministratorCommented:
We often set it as 3600 seconds ~ 1 hour
Frankly, there isn't any "correct" setting.  Whatever setting doesn't impact security at all.  A shorter TTL will result in more DNS queries, but has the advantage that if any change to the record is made, clients will generally be aware of the change sooner.  A longer TTL has the advantage that if the authoritative DNS server for the record is unavailable for a while, fewer clients will generally be impacted.

I say "generally" above, because whether it's a short TTL or long TTL, for a specific client, how long the record has left in the cache before a new query is sent depends on when the last query was the resulted in the record being cached.  In other words, even though a record may have a TTL of 24 hours, at a given time it may have only a few seconds before that time is up and it will have to query the DNS servers again.
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