I don't think it's possible to email each and every mail address of a single domain without knowing the actual adresses.
I mean, it'd be possible if the server you're mailing to was set up to pass every mail send to, for instance,
allaccounts@mailserver.com through to every account. But I doubt there are many servers who support this, understandably because it'd make spamming quite easy.
Anyway, if you do know every single address, then ignore what I said.
