Sendmail, 3rd Edition

Name

$=w

Synopsis

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 ...