My understanding is that the new law still requires a warrant, but that the warrant can be granted by an administrative tribunal rather than a judge - so technically what Fastmail are saying here about only acting on a warrant would be correct.
As per the response from Fastmail, it does still require targeting; the intent of the law appears to be to 'take over' an account and use it to catch conspirators, e.g. "we caught Timmy red-handed planning a terror attack, let's log in as him and tell his co-conspirators to come meet us somewhere, then arrest them all".
Whether or not that's what it will be used for is another question, and a valid concern.
Ugh.
> The police can't intercept, access or modify your messages without us receiving a warrant
So, unlike virtually every other democracy, Australia has granted law enforcement power to surreptitiously modify data owned by others.[1]
> Fastmail remains a privacy-first provider
Does not seem possible unless they move operations to a more privacy-respecting country.
[1] https://news.ycombinator.com/item?id=28364140