Sendmail, 3rd Edition

Relays

A relay is a rule that sends all of one type of mail to a specific destination. One example is email fax transmissions. Clearly, even though local mail should be delivered locally, mail to the pseudouser fax should always be sent to a special fax-handling machine.

The complete list of relays supported by the V8 sendmail mc technique is shown in Table 4-4.

Table 4-4. Relays

Relay	§	Version	Description
BITNET_RELAY	Section 4.5.1	V8.1 and above	The BITNET relay
DECNET_RELAY	Section 4.5.2	V8.7 and above	The DECnet relay
FAX_RELAY	Section 4.5.3	V8.6 and above	The FAX relay
LOCAL_RELAY	Section 4.5.4	V8.1 and above	Relay for unqualified users
LUSER_RELAY	Section 4.5.6	V8.7 and above	Relay for unknown local users
MAIL_HUB	Section 4.5.7	V8.6 and above	All local delivery on a central server
SMART_HOST	Section 4.3.3.6	V8.6 and above	The ultimate relay
UUCP_RELAY	Section 4.5.8	V8.1 and above	The UUCP relay

All relays are declared in the same fashion. For example:

define(`LOCAL_RELAY',`agent:host')

Here, agent is the name of a delivery agent to use, and host is the name of the machine to which all such mail will be relayed. If agent: is missing, it defaults to a literal relay:.

If the host is listed under a domain that uses wildcard MX records (Section 9.3.4), you should specify it with a trailing dot, as, for example:

define(`LOCAL_RELAY', `smtp:relay.sub.domain.')
                                            ↑trailing dot

In Section 19.5 we deal with the flow of rules through the parse rule set ...