Yeah, you either have to use one of our (Fastmail's) domains, or your own domain in which case it's linked to you by the domain registration. Not much choice t

Yeah, you either have to use one of our (Fastmail's) domains, or your own domain in which case it's linked to you by the domain registration. Not much choice there! For sure we recommend (and make it very easy) using your own domain. We want you to stay because we're providing you enough value to be worth staying, not due to lock-in.