[Postfixbuch-users] RFC über das Verhalten von MX-Einträgen?

Reinhard Zierke zierke at informatik.uni-hamburg.de
Do Apr 17 09:21:56 CEST 2008

On Thu, Apr 17, 2008 at 09:05:34AM +0200, Christian Bricart wrote:
> Tach zusammen,
> ich suche ein Dokument (RFC?), in dem steht wie ein fehlender MX-Eintrag
> für einen A-Record behandelt wird/werden soll/werden muss.
> In RFC 2822 hab ich es leider nicht gefunden - oder ich war zu blind... ;-)
> Wir hauen uns gerade die Köpfe darüber ein, ob es einen (im Standard
> definierten!) Fallback auf den Host selber gibt, oder ob das einfach
> stillschweigend von jedem(?) Mailserver gemacht wird...

RFC 2822 bezieht sich auf das Format von E-Mails, nicht auf das Protokoll.
Das tut RFC 2821:

5. Address Resolution and Mail Handling

   Once an SMTP client lexically identifies a domain to which mail will
   be delivered for processing (as described in sections 3.6 and 3.7), a
   DNS lookup MUST be performed to resolve the domain name [22].  The
   names are expected to be fully-qualified domain names (FQDNs):
   mechanisms for inferring FQDNs from partial names or local aliases
   are outside of this specification and, due to a history of problems,
   are generally discouraged.  The lookup first attempts to locate an MX
   record associated with the name.  If a CNAME record is found instead,
   the resulting name is processed as if it were the initial name.  If
   no MX records are found, but an A RR is found, the A RR is treated as
   if it was associated with an implicit MX RR, with a preference of 0,
   pointing to that host.  If one or more MX RRs are found for a given
   name, SMTP systems MUST NOT utilize any A RRs associated with that
   name unless they are located using the MX RRs; the "implicit MX" rule
   above applies only if there are no MX records present.  If MX records
   are present, but none of them are usable, this situation MUST be
   reported as an error.


Reinhard Zierke                       Universität Hamburg, MIN-Fakultät,
zierke at informatik.uni-hamburg.de      Department Informatik
postmaster at informatik.uni-hamburg.de  Vogt-Kölln-Straße 30, D-22527 Hamburg
                                      Tel.: (040) 42883-2295/2276 Fax: -2241

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