If you own the domain, you can just point the MX records to Fastmail/whatever and register to all the different service with, say, service@mydomain.com or you@s

If you own the domain, you can just point the MX records to Fastmail/whatever and register to all the different service with, say, service@mydomain.com or you@service.mydomain.com. No need to set up the addresses or aliases, you can just make them up as you go and deliver everything for mydomain to your inbox.