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Sendmail, 3rd Edition by Bryan Costales

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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. ...

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