Sendmail, 3rd Edition

Relaying

Promiscuous relaying is the process of accepting email from outside your site and then transmitting it to another host also outside your site. Hosts that relay are quickly discovered by spam programs, and used to mask the identity of the originating spam site. Prior to V8.9, promiscuous relaying was allowed by default. Beginning with V8.9, promiscuous relaying is turned off by default.

In place of default relaying, V8.9 and above sendmail provides a variety of features, macros, and databases that allow you to relay in a variety of manners. The access database (Section 7.5) provides a way to relay on a host-by-host, or network basis. Adding domains to the class $=R ($=R) is another method. In this section we describe features that allow you to tune relaying to your taste. Table 7-2 lists the features available as of V8.12.

Table 7-2. Relay features

Feature	§	Description
access_db	Section 7.5	Screen addresses and set policy
loose_relay_check	Section 7.4.2	Allow %-hack relaying
promiscuous_relay	Section 7.4.3	Allow all relaying
relay_based_on_MX	Section 7.4.4	Relay for any site for which you are an MX server
relay_entire_domain	Section 7.4.5	Relay based on $=m
relay_hosts_only	Section 7.4.6	Interpret domains in relay-domains, and access database, as hosts
relay_local_from	Section 7.4.7	Relay if SMTP MAIL domain is in $=w
relay_mail_from	Section 7.4.8	Relay if SMTP MAIL address is RELAY in access database, and provided the entry is properly tagged. ...