Some heavily loaded ISP's have modified daemons that set a lower and upper TTL threshold. Anyone running Unbound DNS can also do this. Some versions and distributions of Java do all manor of odd things with DNS including ignoring TTL's though I do not have a current table of those misbehaving. The same goes for some IoT's but I have no idea what resolver libraries they are using.
Yep. Just checked the docs for that and “cache-min-ttl” is a thing. For those unfamiliar, unbound is a pretty common resolver: it is the default for most BSDs and things based on them (such as pfSense) and used by the popular PiHole and its forks. How common it is to use this setting I can't comment on.
> Some versions and distributions of Java do all manor of odd things with DNS including ignoring TTL's
This at least is less of an issue if all you are futzing with the DNS for is services intended to be consumed by a web browser: if common browsers and DNS resolvers behave OK then you are good, if someone consuming your stuff through their own code hits a problem they can work around it themselves :)
It goes without saying that only a fool would play trick like this for email as that is already a mountain of things that can be easily upset by anything off the beaten track.
The reason I mention Java is that when updating DNS in a business, there may be business to business flows that are critical. This is becoming more common than ever with cloud-to-cloud-to-cloud dependencies. Mishaps in cloud services can affect a service used by a large number of people. That is why I always tried to teach people to design apps so that TTL could in theory be 1 week and it would not matter. e.g. apex domain anycast IP used for authentication, then direct browsers, API clients and cloud daemons to a service dedicated domain name that is also anycast and uses health checks behind the scenes to take nodes out the picture rather than relying on DNS.
Some heavily loaded ISP's have modified daemons that set a lower and upper TTL threshold. Anyone running Unbound DNS can also do this. Some versions and distributions of Java do all manor of odd things with DNS including ignoring TTL's though I do not have a current table of those misbehaving. The same goes for some IoT's but I have no idea what resolver libraries they are using.