iX 6.5)

138 Chapter8

DNS BIND/iX

DNS and Electronic Mail

One of the advantages of the Domain Name System over host tables is

its support of advanced mail routing. DNS offers a mechanism for

specifying backup hosts for mail delivery. The mechanism also allows

hosts to assume mail handling responsibilities for other hosts. This lets

diskless workstations that don’t run mailers, for example, have mail

addressed to them processed by their server. These features give

administrators more ﬂexibility in conﬁguring electronic mail on their

network.

MX Records

DNS uses a single type of resource record to implement enhanced mail

routing, the MX record. MX records specify a mail exchanger for a

domain name, a host that will either process or forward mail for the

domain name.

In order to prevent mail routing loops, the MX record has an extra

parameter, besides the domain name of the mail exchanger, a

preference value like: peets.mpk.ca.us IN MX 10 relay.hp.com

speciﬁes that relay.hp.com is a mail exchanger for peets.mpk.ca.us

at preference value 10.