On 2025-08-22 00:05:37 (+0600), L. Mark Stone via mailop wrote:
Would you all agree that it's not short TTLs per se that are causing
issues, but rather, it's some combination of network latency, DNS
server performance and (Microsoft's) configuration for how long it
will wait for a DNS query to complete?
IOW, if you are doing just one lookup a day (86400), and the average
lookup failure rate is say 5%, then you'll have a delivery issue once
every 20 days.
But with a TTL of 300, you can reasonably expect to have multiple
delivery issues every day, given that same 5% error rate.
This holds for all DNS queries -- not only email. This is precisely why
DNS nerds tell everyone to set their TTLs higher in regular operations.
The only reason you might want a lower TTL is during a migration or if
you're using DNS as a poor man's load balancing solution.
All of this then seems to auger for hosting one's DNS on robust
infrastructure behind a low-latency, low-jitter, high-bandwith
connection as close as possible to the Internet backbones.
Do you agree?
For most applications you don't really need low latency, low jitter or
high bandwidth. You only need it to be reliable. It doesn't matter if
it takes a couple of seconds to resolve a domain if the result is going
to be cached for a day.
As far as the DNS is concerned: reliability is much more important than
any other metric. It has to work.
Philip
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