I do the exact same thing on fastmail and it works seamlessly -- I pretty much use domain@my-address.com for every site I sign up for. The only trick is you do

I do the exact same thing on fastmail and it works seamlessly -- I pretty much use domain@my-address.com for every site I sign up for. The only trick is you do have to configure configure the addresses if you want to send (not receive) mail from $recipient@your-domain.com. I use the standard plan.