ttavoy The old version was at least comprehensible, though it was also puzzling (how could one tell that the destination domain is hosted at Opalstack and why would that make a difference?)
By this we're referring to your own domains, so you're the one who'll know whether or not they are using Opalstack's email service.
It mattered because, for example, if your sent yourself mail from ceo@domain.com to all@domain.com, and you had not added ceo@domain.com as an address, then the message would not be sent because our SMTP would not recognize it as a valid sender address.
As it turns out, that was a misunderstanding on the part of our documentation author (my bad). The only requirement is that you've got the domain added to your account.
ttavoy "domains that you own" : me personally? what if my relative owns them?
"added to your Opalstack dashboard" : I just added example.com to my Opalstack dashboard ... have I done something illegal and/or immoral?
By "domains that you own" we mean the domains that you have the legal right or permission to use with your Opalstack servers. We're trusting our customers to do the right thing. 🙂
If you choose to do the wrong thing, well you can add example.com, but it's not going to matter unless example.com is using our NS. If we received some sort of complaint from the owner of example.com we'd reach out to you to sort it out.
The better solution to that problem is to verify domain ownership before we publish DNS records or allow mail to be sent from a particular domain. At this time we don't verify domain ownership for the domains that you add but it's something we're considering.