tl;dr: The law passed doesn't affect FastMail at all, and your data is at least as private with FastMail as it is with Gmail, which also responds to lawful government requests for your data.
My point is that the impact of storing your email with an Australian company is not in itself a problem or increased compromise in your privacy.
However I'm concerned that the Australian government (given their recent authoritarian actions) might be a little too quick to request my data from FastMail.
If you have very strong concerns about the government requesting your data, you should look at end-to-end solutions like ProtonMail.
As for ProtonMail: Yes, I've been a ProtonMail customer for about half a year now. However I'm really dissatisfied on a number of ends:
<opinion>
- the bridge is a bad solution and it doesn't work well
- the bridge doesn't exist on Android, tying me into their own client
- their own client is proprietary and has GSF dependencies (optional, but still - privacy?)
- (this might be due to technical constraints so it might be not valid but) they generally seem to have an aversion against standards
- their technical team is slow and deadlines are (from what I've seen) meaningless
- (possibly FUD but) the recent drama [1]
</opinion>
Don't get me wrong they're doing important work. And I believe them in the sense that they can do cryptography well and they're bringing (a good amount of) privacy to the masses. But they're not less problematic than any other major provider I'm aware of.
In the end it boils down to everything sucks™.
[1] https://steigerlegal.ch/2019/05/23/protonmail-real-time-surv...