[awayand]

you can set things up much, much easier, fastmail calls it subdomain aliasing or something like that.

Basically, it allows you to create email aliases without having to whitelist.

Setup [e-mail] and reject everything else arriving there.

Accept anything at @i.yourdomain.com

I have an inbox, everything [e-mail] arrives there.

Then I have an "other" mailbox where all the @i.yourdomain.com emails arrive.

If there is a really annoying website that doesn't respect my wishes I create a filter for the offending email to ban any mail to my spam folder.