domain
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... to route a message addressed to a given Internet domain name. This
involves a discussion of how mailers interpret MX RRs ...
...
Under domains, one cannot simply open a connection to LOKI.BBN.COM,
but must instead ask the domain ...
... domains, one cannot simply open a connection to LOKI.BBN.COM,
but must instead ask the domain system where messages to LOKI.BBN.COM
are to be delivered. And the domain system may direct a mailer to
...
... but must instead ask the domain system where messages to LOKI.BBN.COM
are to be delivered. And the domain system may direct a mailer to
deliver messages to an entirely different host, such as SH.CS ...
... What the Domain Servers Know ...
... (RRs), each of which contains a particular piece of information about
a given domain name (which is usually, but not always, a host). The
simplest way to think of a RR ...
... host). The
simplest way to think of a RR is as a typed pair of datum, a domain
name matched with relevant data, and stored with some additional type
information to help systems determine when the RR is relevant. For
...
... RRs known as MX
RRs. Each MX matches a domain name with two pieces of data, a
preference value (an unsigned 16-bit integer ...
... CNAME) RR, which simply states that the
domain name queried for is actually an alias for another domain name,
which is the proper, or canonical ...
... RR, which simply states that the
domain name queried for is actually an alias for another domain name,
which is the proper, or canonical, name; and the Well Known Service ...
... routing information
is out of date or incomplete. Out of date information is only a
problem when domain tables are changed. The changes will not be
known to all affected hosts until their resolver caches ...
... caches
flushed. In other words, given proper precautions, mail looping as a
result of domain information should be avoidable, without requiring
mailers to query authoritative servers. (The appropriate precaution
...
...
The incomplete data problem also requires some care when handling
domain queries. If the answer section of a query is incomplete
...
... RRs may be left out. This may result in mail looping, or
in a message being mistakenly labelled undeliverable. As a result,
mailers may only accept responses from the domain system which have
complete answer sections. Note that this entire problem can be
avoided by only using virtual circuits ...
... situation is likely to be very rare and datagrams are the preferred
way to interact with the domain system, implementors should probably
just ensure that their mailer will repeat a query ...
... is discussed in terms of the problem of a mailer on a host with
domain name LOCAL trying to deliver a message addressed to the domain
name REMOTE. Both LOCAL and REMOTE are assumed to be syntactically
...
... host with
domain name LOCAL trying to deliver a message addressed to the domain
name REMOTE. Both LOCAL and REMOTE are assumed to be syntactically
correct domain names ...
... domain
name REMOTE. Both LOCAL and REMOTE are assumed to be syntactically
correct domain names. Furthermore, LOCAL is assumed to be the
official name for the host on which the mailer resides (i.e., it is
...
... for REMOTE. It is strongly urged that this step be taken every time
a mailer attempts to send the message. The hope is that changes in
the domain database will rapidly be used by mailers, and thus domain
...
... the domain database will rapidly be used by mailers, and thus domain
administrators will be able to re-route ...
...
Getting no response to the query. The domain server the mailer
queried never sends anything back. (This is distinct from an
answer which contains no answers to the query, which is not an
...
... probably be treated differently. For example, a response code of
"non-existent domain" should probably cause the message to be
returned to the sender as invalid, while a response code ...
... RR, it indicates that REMOTE is actually an alias
for some other domain name. The query should be repeated with the
canonical ...
... aliases, its answer section should be a (possibly zero
length) list of MX RRs for domain name REMOTE (or REMOTE's true
domain name if REMOTE was a alias ...
... RRs for domain name REMOTE (or REMOTE's true
domain name if REMOTE was a alias). The next section describes how
this list is interpreted.
...
... delivering a message is mentioned, all that is meant is that the
mailer should do whatever it needs to do to transfer a message to a
remote site, given a domain name for that site. (For example, an
SMTP mailer will try to get an address ...
... SMTP mailer will try to get an address for the domain name, which
involves another query to the domain ...
... domain name, which
involves another query to the domain system, and then, if it gets an
address, connect to the SMTP ...
... network to the address associated
with a given domain name is not within the scope of this memo.
...
... MX). In addition, the mailer should do no further processing on the
list, but should attempt to deliver the message to REMOTE. The idea
here is that if a domain fails to advertise any information about a
particular name we will give it the benefit of the doubt and attempt
delivery ...
...
For each MX, a WKS query should be issued to see if the domain
name listed actually supports the mail service desired. MX RRs
...
... service desired. MX RRs
which list domain names which do not support the service should be
discarded. This step is optional, but strongly encouraged.
...
... delivery to REMOTE's address (if it exists) before returning
the message. Another, more dangerous, possibility is that the domain
system believes that LOCAL is handling message for REMOTE, but the
mailer on LOCAL is not set up to handle mail for REMOTE. For
...
... system believes that LOCAL is handling message for REMOTE, but the
mailer on LOCAL is not set up to handle mail for REMOTE. For
example, if the domain system lists LOCAL as the only MX for REMOTE,
LOCAL will delete ...
... LOCAL will delete all the entries in the list. But LOCAL is
presumably querying the domain system because it didn't know what to
do with a message addressed to REMOTE. Clearly something is wrong.
How a mailer chooses to handle these situations is to some extent
...
... network
which simply state that any mail to a domain is to be routed through
a relay. For example, at the time that this RFC is being written, all
mail to hosts ...
... a relay. For example, at the time that this RFC is being written, all
mail to hosts in the domain IL is routed through RELAY.CS.NET. This
is done by creating a wildcard ...
... of RELAY.CS.NET. This should be transparent to the mailer since the
domain servers will hide this wildcard match. (If it matches *.IL
with HUJI.IL for example, a domain ...
... domain servers will hide this wildcard match. (If it matches *.IL
with HUJI.IL for example, a domain server will return an RR
containing HUJI.IL, not *.IL). If by some accident a mailer receives
...
... route through. This decision making is outside the scope of this
memo, although mailers may well use the domain system to help them
decide. However, once a mailer decides to deliver a message via the
Internet ...