sendmail, 4th Edition

FEATURE(relay_entire_domain)

By default, only hosts listed in the access database (The access Database on page 277) with the righthand side keyword RELAY, or hosts that are listed with the RELAY_DOMAIN macro (The RELAY_DOMAIN mc macro on page 269), are allowed to relay mail through the local host. You can allow all the hosts in your domain to relay mail through the mail server by listing them there, but it is much easier to use the shorthand method provided by the FEATURE(relay_entire_domain):

FEATURE(`relay_entire_domain')

When you define this feature, you enable any host listed in the class $=m (which contains your domain; $=m on page 872) to relay mail through the local host. Note, however, that if your host is named something such as bob.gov, your host and domain will be the same. Whatever you do, never put a top-level domain such as gov, or com, or de into $=m, or you will find your site relaying mail for any host in that top-level domain.

Note that $=m should not be used to have mail accepted as local under a variety of domains. Instead, use the FEATURE(domaintable) (FEATURE(domaintable) on page 621).