| axp165.det.dec.com does _not_ have any MX records:
$ nslookup -query=MX axp165.det.dec.com
Server: localhost
Address: 127.0.0.1
*** No mail exchanger information is available for axp165.det.dec.com
"det.dec.com" _does_ have MX records, but it has 3 equal-priority hosts
at the top of the preference list (axp165, kamet, and illusion).
Neither of those other 2 hosts has any MX records either, so the only
way anybody on any of those 3 hosts can get mail from the outside is
via "[email protected]". Mail sent that way will arrive randomly at one
of the 3 hosts.
With that configuration, all 3 of those hosts have to have aliases
defined ( user: user@actualhost ) for every user on at least each of
the other 2 or will have to be in the same NIS domain and use an NIS
aliases map that aliases every user in the NIS domain to an address
with an actual host name. In addition, sendmail.cf on all 3 of those
hosts has to be set up to masquerade return addresses sent from those
hosts as being from "[email protected]" and to have a host alias (Cw)
that includes "det.dec.com". This, however, doesn't do anything for any
other host in det.dec.com that lacks MX records. If there are others,
those hosts would also have to masquerade outbound mail as being from
[email protected] and users on those hosts would also have to be added
to the aliases on each of the 3 det.dec.com hosts (axp165, kamet, and
illusion).
A more usual way of configuring the systems would be to have MX records
defined for each host in the det.dec.com domain with the host itself as
priority 1 (for example), zero or more site relays as a lower priority,
and one or more firewall gateways as the lowest priority (highest
number). The MX records for det.dec.com would have 1 highest-priority
host that handles aliases for anything addressed to [email protected]
and a number of lower-priority hosts, including at least one firewall
gateway host. In that case, only the single host servicing
[email protected] addresses (if any) need have det.dec.com as a host
alias in its sendmail.cf, and no host needs to masquerade outbound
addresses (although they may). Other hosts need worry only about their
own users.
-Tom
|