Before the sendmail
program reads its configuration file, it calls
gethostbyname(3) or
getipnodebyname(3) to find all the known aliases
for the local machine. The argument given to
gethostbyname(3) or
getipnodebyname(3) is the value of the
$w macro that was derived from a call to
gethostname(3) ($w).
Depending on the version of sendmail you are
running, the aliases that are found will be either those from your
/etc/hosts file or those found as additional
A or AAAA records in a DNS
lookup. Then, depending on the DontProbeInterfaces
option (DontProbeInterfaces), sendmail
will round out that picture by examining (probing) each network
interface and extracting from it the associated IP address or
hostname.
To see the aliases that sendmail found, or to
see what it missed and should have found, use the
-d0.4 debugging switch (-d0.4). Any aliases that are found are printed as:
aka: alias
Depending on your version of sendmail, each
alias is either a hostname (such as
rog.stan.edu) or an IPv4 address (such as
[123.45.67.8]), or an IPv6 address (such as
[IPv6:2002:c0a8:51d2::23f4]).
Many sendmail.cf files use the
$=w class macro to
define all the ways users might reference the local machine. This
list must contain all names for the local
machine as given in the /etc/hosts file, all
names for the local host as listed in DNS (including CNAME and MX
records), and the names associated with your network interfaces. For
example:
# All our routing identities
Cw server1 server2
# All our local aliases
Cw localhost mailhost tops-link print-router loghost
# DNS records
Cw serv-link
# We are a bitnet registered node
Cw bitserver
The correct way to add these domains to $=w in
your mc file is with LOCAL_DOMAIN, like this:
LOCAL_DOMAIN(`server1 server2')
LOCAL_DOMAIN(`localhost mailhost tops-link print-router loghost')
LOCAL_DOMAIN(`serv-link')
LOCAL_DOMAIN(`bitserver')
Another correct way to add hostnames to class $=w
is with the use_cw_file feature (FEATURE(use_cw_file)).
In addition to hostnames, you can also add addresses to the
$=w class. To do so, just surround each address
with square braces:
LOCAL_DOMAIN(`[123.45.67.8]') 
IPv4 address
LOCAL_DOMAIN(`[IPv6:2002:c0a8:51d2::23f4]') IPv6 address
Note in the second example that you must prefix any IPv6 addresses
with a literal IPv6: expression. That prefix
signals to sendmail that it is dealing with an
IPv6 address.
