You can also do this with Gmail aliases[0]: "For example, messages sent to jane.doe+notes@gmail.com are delivered to jane.doe@gmail.com." Although the number of sites with incorrect email validation (that reject perfectly valid email addresses) is shocking. I do this, and you can then just block the alias if it starts recieving spam.
With fastmail you can also use subdomain addressing [0] for those broken sites and to prevent people from filtering (\+[^@]+) to get unmarked addresses. user@sub.domain.tld is handled the same way as user+sub@domain.tld
While it may have worked in the past (for a while anyway), what exactly prevents spammers from stripping the suffix, given that the functionality has been public knowledge for many years? Best case they'll be lazy and try both with and without, and you'll end up knowing. Blocking the alias cannot possibly have any effect.
> Blocking the alias cannot possibly have any effect.
Ah, but it does work (for me, twice). Of course spammers could strip the suffix. But since spam is a numbers game, I'm not sure it's worth the effort for them.
[0] https://support.google.com/mail/answer/12096?hl=en