On Mon, Jul 06, 1998 at 10:24:27PM -0300, David Maxwell wrote:
> The RFCs specifically state that an MTA MUST NOT accept a message unless
> it can guarantee being able to return error messages. By using a From: address
> with a host portion which has no MX, the mailer cannot be assured of its 
> ability to return errors.

I really hate to be like this...
...but if a host has an A record, then isn't an MTA connected to by that
host guaranteed to be one to which errors can be returned?

If not, I suspect that that violates another provision of the RFCs
somewhere, and if not that, then fixing that would seem to be more
productive than adding an otherwise spurious requirement that every host
capable of sending mail be covered not only by an A record (which implies an
associated PTR record), but an MX record as well.

> P.S. The world would contain a lot less spam if everyone configured their
> DNS fully/properly and required things like this.

This is the first I've ever heard of an MX record being other than purely an
optional way of collecting incoming mail on one machine for processing. I
suspect I'm far from alone. If an MX record is suddenly being defined as
being required, I would think it should be shouted from the rooftops...