Review IANA and remaining IESG feedback on rfc5321bis

Review currently open tickets on A/S, as well as rfc5321bis feedback that might affect it
<https://datatracker.ietf.org/doc/draft-ietf-emailcore-as/>. See
<https://github.com/ietf-wg-emailcore/emailcore/labels/component_email-applicability-statement>
for the list of issues.