All recipient addresses are rewritten by rule set 2 and the
R=
of delivery agents. But in almost all configuration files,
rule set 2 is unused because no processing is needed:
# Recipient processing: none needed S2
But note that rule set 2 can be used to debug rules. [5] Consider the following rule in rule set 2:
[5] This is a truly bogus example. We are really stretching to find a use for rule set 2. There is no reason to do this debugging in rule set 2 because rule set 99 would work just as well. According to Eric, "I can think of no good reason to use
S2
today."
R$#$+ $:$+ $:$2 Strip delivery agent and host when debugging
Recall that rule set 0 returns a triple. When testing an address,
rule set 2 can be called following rule set 0 to simulate
the rewriting of the user portion of rule set 0. Here the
LHS matches only a triple, so normal recipient addresses
are unaffected. The user part that is returned by the RHS can then
be used to test individual R=
rules of delivery agents.
(Another technique is to use the /try
command in
-bt
rule-testing mode; see Section 38.5.6, "Try a Delivery Agent with /try".)