11.7 Rule Set 1

When we began this chapter, we explained that the sender's address was processed by a series of three rule sets: rule set 3, rule set 1, and the custom rule set specified by the S= delivery agent equate. We've described rule set 3 and S=, but we haven't yet described rule set 1. If we send all mail to a central hub, we don't really need a rule set 1. That's because there is nothing that we need to do to all sender addresses. In fact, most configuration files, even at large sites, have no need for a rule set 1. [4]

[4] Eric says, "Given it to do over, rule sets 1 and 2 wouldn't exist."

Still, it is wise to add a dummy rule set 1 (one that does nothing) to the client.cf file. For one thing, this makes it clear that you haven't simply omitted rule set 1 by oversight. It also allows us to illustrate some points about rule sets in general.

R$-             $@ $1@${HUB}            user -> user@hub
R$-@$w          $@ $1@${HUB}            user@local -> user@hub
 
S1 # Generic sender rewrite (unused)                                  new

We place rule set 1 last in the client.cf file, as we will continue to do with any other unused rules. This declaration of rule set 1 illustrates three points about rule sets in general:

• Rule sets do not have to be in any particular order in the configuration file. The sendmail program reads the entire file and sorts the rule sets internally.

• A rule set containing no rules is a "do-nothing" rule set. The workspace passed to it is returned unchanged.

• Rule sets that are declared but unused should be commented to indicate this fact.

The positioning of rule sets in the configuration file is largely a matter of individual taste. Some administrators like to keep custom rule sets (such as Hubset) next to the delivery agent definition rather than with the general rules. We don't favor any particular approach over another. The overriding concern in any configuration file - which can be complex - should be for clarity and organization.