A Simple Rule Pattern Example To better see
A Simple Rule Pattern Example To better see how the macro substitution patterns operate, consider the following rule lefthand side: $* < $+ > This rule matches Zero or more tokens, followed by the < character, followed by one or more tokens, followed by the > character. If this rule were applied to brewer@vbrew.com or Head Brewer < >, the rule would not match. The first string would not match because it does not include a < character, and the second would fail because $+ matches one or more tokens and there are no tokens between the <> characters. In any case in which a rule does not match, the righthand side of the rule is not used. If the rule were applied to Head Brewer < brewer@vbrew.com >, the rule would match, and on the righthand side $1 would be substituted with Head Brewer and $2 would be substituted with brewer@vbrew.com. If the rule were applied to < brewer@vbrew.com > the rule would match because $* matches zero or more tokens, and on the righthand side $1 would be substituted with the empty string. Ruleset Semantics Each of the sendmail rulesets is called upon to perform a different task in mail processing. When you are writing rules, it is important to understand what each of the rulesets are expected to do. We’ll look at each of the rulesets that the m4 configuration scripts allow us to modify: LOCAL_RULE_3 Ruleset 3 is responsible for converting an address in an arbitrary format into a common format that sendmail will then process. The output format expected is the familiar looking local-part@host-domain-spec. Ruleset 3 should place the hostname part of the converted address inside the < and > characters to make parsing by later rulesets easier. Ruleset 3 is applied before sendmail does any other processing of an email address, so if you want sendmail to gateway mail from some system that uses some unusual address format, you should add a rule using the LOCAL_RULE_3 macro to convert addresses into the common format. LOCAL_RULE_0 and LOCAL_NET_CONFIG Ruleset 0 is applied to recipient addresses by sendmail after Ruleset 3. The LOCAL_NET_CONFIG macro causes rules to be inserted into the bottom half of Ruleset 0. Ruleset 0 is expected to perform the delivery of the message to the recipient, so it must resolve to a triple that specifies each of the mailer, host, and user. The rules will be placed before any smart host definition you may include, so if you add rules that resolve addresses appropriately, any address that matches a rule will not be handled by the smart host. This is how we handle the direct smtp for the users on our local LAN in our example.
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