I’m not happy when I see someone technical quoting a time in summer (eg during daylight savings) which claims to be “AEST”.

It’s almost certainly actually AEDT.

A summary of the abbreviations, which looks reasonably official, is here: Australian timezones.

In summary, AEST, ACST and AWST apply in winter. AEDT, ACST and AWST apply in summer.

The other issue I had with a recent email was it said 12:00pm AEST. I think in this context, they meant midnight AEDT, but it’s confusing. Better to either say Midnight, or use 24-hour time: 00:00.