Tyvm! That looks epic. Link: https://www.fastmail.com/help/receive/addressing.html Might be tricky if the time came to migrate away from FastMail though.

Indeed! This is why I stopped using it. I love Fastmail, but who knows if I feel that way in 5 years. The entire point of Fastmail + own domain is never being locked in again. Using subdomain addressing locks you in once again.

I'm with @rb666; Don't rely on it as most will support plus+ addressing but not the the fast mail subdomain addressing as I am now in the process of migrating to Migadu.com and I need to go and unsubscribe and resub using the plus+tag. It's a PITA... lesson learned, stick with best industry practices even if there is an easier method because you'll thank yourself later.

Is also nicer than plus-notation like [email protected], which from time to time gets rejected by some overly zealous (but wrong) adress checking tool.

catchalls are great. In addition to allowing the use of arbitrary custom addresses on a whim they make it really easy to identify spam and train spam filters. Anything that arrives on multiple random/unused addresses at your domain is spam.