When I get spam to a particular alias, I blacklist it to my spam folder. Naturally this might get a little difficult if a spam bot ever figures this out where I'd need to move to a whitelist rather than blacklist process. But it's worked flawlessly for years so far.
At least with my method I don't need to create the alias in advance.
https://www.fastmail.help/hc/en-us/articles/1500000277942-Ca...
When I get spam to a particular alias, I blacklist it to my spam folder. Naturally this might get a little difficult if a spam bot ever figures this out where I'd need to move to a whitelist rather than blacklist process. But it's worked flawlessly for years so far.
At least with my method I don't need to create the alias in advance.