[Mimedefang] OT: DNS sanity check

[John Rudd]

Les Mikesell wrote:

> 
> And you seem to have avoided reading the other part of what I quoted
> saying how hosts that are not in DNS _at all_ are permitted with special
> dispensation in the syntax.  I don't see how anyone who has read that
> can claim that is a requirement for forward or reverse DNS support at
> the sending host.
> 

Show me where RFC 2821 says that the receiver _MUST_ grant the
alternative, as opposed to it being a means of how to handle the
situation if the receiver decides to allow the alternative.

4.1.3 does not say "you must accept messages from hosts without DNS
entries".  It describes what an address literal should look like
_in_case_ you decide to accept messages from hosts without DNS.