Edit: oh god, leaving this in place for posterity but I am completely misrepresenting fastmail here. It is protonmail that I recently tried and had these limitations. Apologies! How embarrassing. Also, I have no idea why the child comment correcting me would be so downvoted. It’s apparently correct.
Yes, but fastmail has a couple dealbreaker limitations when doing this: First, you can’t originate mail from that address; you can only respond. This makes it unusable for a lot of mailing list control messages and other systems where you are required to make inquiries from a registered email address. Second, you must explicitly set up each of the unique recipient addresses, which is a huge burden when you want to be able to generate them on the fly when signing up for web accounts (and when you already have hundreds in use because you’ve spent decades giving every company a unique address).
If they addressed these and I could have an unlimited number of suffixes directed to a single fastmail address, I’d sign up for a paid account in a heartbeat. Looks like a great service but those are fatal flaws IMO.
