With both capability and failure notification, we concluded that there had to
be a third party to get extensions from and to make notes of failure on. It
was noted that due to the nature of the game, we were doomed to having a third
party (not delivery server, not client) that holds extension and failure
information;
Envelope-matching command should take similar commands to address match: :localpart / :domain / :all
This also requires parts of an 822 parser, but less of them (see above).