16.3. A Limitation of MX Records
While we are on the topic of
MX records, let's talk about how they can result in mail taking
a longer path than necessary. The MX records are a list of data
returned when the domain name of a mail destination is looked up. The
list isn't ordered according to which exchanger is closest to
the sender. Here is an example of this problem. Your
non-Internet-connected network has two hosts capable of relaying
Internet mail to your network. One host is in the U.S., and one host
is in France. Your network is in Greece. Most of your mail comes from
the U.S., so you have someone maintain your zone and install two
wildcard MX records -- the highest preference to the U.S. relay
and a lower preference to the relay in France. Since the U.S. relay
is at a higher preference,
all mail will go
through that relay (as long as it is reachable). If someone in France
sends you a letter, it will travel across the Atlantic to the U.S.
and back because there is nothing in the MX list to indicate that the
French relay is closer to that sender.
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| 16.2. Wildcards |  | 16.4. Dialup Connections |
