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    SubjectRe: DNS goofups galore...
    "Henning P. Schmiedehausen" <> writes:

    > (H. Peter Anvin) writes:
    > >> In other words, you do a lookup, you start with a primary lookup
    > >> and then possibly a second lookup to resolve an MX or CNAME. It's only
    > >> the MX that points to a CNAME that results in yet another lookup. An
    > >> MX pointing to a CNAME is almost (almost, but not quite) as bad as a
    > >> CNAME pointing to a CNAME.
    > >>
    > >There is no reducibility problem for MX -> CNAME, unlike the CNAME ->
    > >CNAME case.
    > >Please explain how there is any different between an CNAME or MX pointing
    > >to an A record in a different SOA versus an MX pointing to a CNAME
    > >pointing to an A record where at least one pair is local (same SOA).
    > CNAME is the "canonical name" of a host. Not an alias. There is good
    > decriptions for the problem with this in the bat book. Basically it
    > breaks if your mailer expects one host on the other side (
    > and suddently the host reports as The sender is
    > allowed to assume that the name reported after the "220" greeting
    > matches the name in the MX. This is impossible with a CNAME:
    > IN A
    > IN CNAME
    > IN MX 10
    > % telnet smtp
    > 220 ESMTP ready
    > ^^^^^^^^^^^^
    > This kills loop detection. Yes, it is done this way =%-) and it breaks
    > if done wrong.

    This is humour, yeh ?

    I would be supprised if even sendmail assumed braindamage like the
    For instance something that is pretty common is... IN A IN MX 10 IN MX 20

    ; This is really IN A

    ...another is to have "farms" of mail servers (the A record for the MX
    has multiple entries).
    If it "broke" as you said, then a lot of mail wouldn't be being routed.

    # James Antill --
    * ^From: .*james@and\.org
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