29.8 Rule Set 2

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".)