In my experience no one really uses ST/DT properly in the US in casual email… in fact I can’t remember the last time I received a human-written email referencing EDT or PDT. For some reason everyone just defaults to PST/EST.

I’ve given up even trying and just use “PT” and “ET” or even “NYC time” or “SF time” especially when interacting with those outside the US (who are less familiar with the custom and more confused when a mistake is made).

With my team I only use UTC. Specially because most of us are not in the US.

It's common to use the same time zone abbreviation throughout the year. E.g. in Europe you'd be on CET or CEST depending on time of year, but it's common enough to use "CET" for both that it's a de facto standard. Not a hill to die on at this point.

CET in this informal way means "CET OR CEST depending on which of them is current at the location at the given time".

This can give rise to ambiguity in places, but it's pretty rare that it does.

Most people don't know what PST is and just use it all year without thinking about it.

They likely meant to put “PT” which merely indicates Pacific Time ignoring if the time zone is in daylight savings or not.

I see this a lot.

I always want to correct people on it. But unfortunately it resides in funky middle-ground between (a) corrections being welcome / helpful and (b) corrections seeming nit-picky / pedantic.

Similarly to misuses (according to classical grammar rules) of "who" vs. "whom".

Both grate on me, but there's no acceptable way to get others to change.