On Thu, 20 Nov 2003, John Dalbec wrote:
> >>What RFC allows an MX record (example.com -> mail.example.com say) to exist
> >>without an A record for example.com existing?
> >
> >
> > No RFC forbids such behaviour.
> >
>
> Is there an RFC that forbids MTA's from rejecting mail to/from
> postmaster@??? because of the above DNS?
Yes. Or at least, there's an RFC that says you MUST support it. RFC 2821
says this:
----------------------------------------------------------------------------
4.5.1 Minimum Implementation
In order to make SMTP workable, the following minimum implementation
is required for all receivers. The following commands MUST be
supported to conform to this specification:
EHLO
HELO
MAIL
RCPT
DATA
RSET
NOOP
QUIT
VRFY
Any system that includes an SMTP server supporting mail relaying or
delivery MUST support the reserved mailbox "postmaster" as a case-
insensitive local name. This postmaster address is not strictly
necessary if the server always returns 554 on connection opening (as
described in section 3.1). The requirement to accept mail for
postmaster implies that RCPT commands which specify a mailbox for
postmaster at any of the domains for which the SMTP server provides
mail service, as well as the special case of "RCPT TO:<Postmaster>"
(with no domain specification), MUST be supported.
----------------------------------------------------------------------------
However, RFCs are not laws. You cannot compel anybody to comply with
their requirements (unless they have legally contracted with you to do
so). The underlying condition for RFCs is always "If you want to
interwork successfully with most of the other hosts on the internet,
then ...".
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
Get the Exim 4 book: http://www.uit.co.uk/exim-book
