You can use a wildcard for this: https://www.fastmail.com/help/receive/alias-catchall.html

I used to manually create them, then I learned of this and it's been a time saver.

This is no good when you want to use the fastmail domain for the aliases. Ever since the twitter @N theft[1], I've learned to never use a custom domain email when signing up for anything. It just increases your attack surface. I prefer to leave it to fastmail to protect their own domain from hijacking.

[1] https://arstechnica.com/information-technology/2014/01/picki...

You could forward all mail from a Gmail address to Fastmail, and then use [email protected] for each service you use. Might be considered security through obscurity, but if nobody knows your actual email domain except for the Gmail address, less likely to have it attacked. Goes without saying to protect that Gmail account at all costs though.

If you only want to receive mail at aliases it's easy: just setup an email catch-all on your domain ;-) To send is another matter; and unfortunately, I haven't found a way to easily do this with fastmail.

Just create a wildcard identity to match (*@yourdomain.com) – when you select this in compose, you will be able to edit the address.

You can use the plus system.

[email protected]

Tried that, once. I wish they had a simple web api for this.