I have similar feeing for Gmail (it's effective anti spam engine), google maps and google docs (which pioneered shared docs. It feels outdated on many fronts now, but it was a pioneer).
anti-spam is only an issue if people dump their email anywhere.
I usually register my mail on webpages as first.last+webpage@mail.com and once they would spam this mail, it gets blacklisted.
I literally get only 1-3 real spam mails per month without any filter.
I see this recommendation everywhere and I am genuinely surprised that it works. Any spammer can find out your real address since there is an obvious mapping from + addresses to your real address. An actual solution would hide this mapping.
Yeah. Fastmail masked addresses are random. The best you can do is guess that an address might be masked, due to it not being johnsmith@fastmail.com, but it provides no information about your real email address.