Sendmail, 3rd Edition

The parse Rule Set 0

The job of the parse rule set 0 is to select a delivery agent for each recipient. Beginning with V8.10 sendmail, it is declared like this:

Sparse=0

As the name parse implies, the job of this rule set is to parse an address into important information so that the final form of delivery can be determined.

The parse rule set 0 is called once for each recipient and must rewrite each into a special form called a triple. A triple is simply three pieces of information: the symbolic name of the delivery agent, the host part of the address, and the address to be passed to the delivery agent. Each part is indicated in the RHS by a special prefix operator, as shown in Table 19-1.

Table 19-1. Rule set 0 special RHS operators

Operator	Description
$#	Delivery agent
$@	Recipient host
$:	Recipient address (e.g., for $#smtp, $: has user@host)

The triple is formed by rewriting with the RHS. It looks like this:

$#delivery_agent $@ host  $: address

The delivery agent selection must be the first of the three. In addition to specifying the delivery agent, $# also causes the parse rule set 0 to exit. The other two parts of the triple must appear in the order shown ($@ first, then $:).

All three parts of the triple must be present in the RHS. The only exception is the $@ host part when the delivery agent has the F=l flag set. It can be present for V8 sendmail but must be absent for all other versions of sendmail.

Not all rules in the parse rule set 0 are specifically used to select ...