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From: nelson@sun.soe.clarkson.edu (Russ Nelson)
Newsgroups: comp.mail.sendmail
Subject: The algorithm for rewriting rules
Message-ID: <1990May31.152505.28721@sun.soe.clarkson.edu>
Date: 31 May 90 15:25:05 GMT
Article-I.D.: sun.1990May31.152505.28721
Reply-To: nelson@clutx.clarkson.edu
Organization: Clarkson University, Potsdam, NY
Lines: 54

A ruleset is like a subroutine that sendmail calls when it wants an
address transformed.  Sendmail calls rules 0 through 4 (or 6,
depending on your version) by itself.  You can call other rulesets as
subroutines.  Specific mailers can call rulesets for the sender or
recipient.

I can't find the algorithm for the application of the rewriting rules.  As
best I can determine from a source, this is it:

	Apply a rule.
	If it matches, rewrite it and apply the same rule again.
	If it doesn't match, try the next rule.

	If you start a RHS with $:, then after rewriting, apply the NEXT rule.
	If you start a RHS with $@, then after rewriting, exit this ruleset.
	If you start a RHS with $#, then after rewriting, exit this ruleset,
	  and ruleset zero will see the $#, and use that information to deliver
	  the mail using the given mailer.


	The picture given in the documentation that looks roughly like this:


          /----> 0 ----> resolved address
          |
 	  |           /---> 1 ---> S ---\
    	  |           |			|
  --> 3 ----->  D  ---|			|---> 4 ----> Message
		      |			|
                      \---> 2 ---> R ---/


	is terribly misleading.  It should really looks like this:



 ---> 3 -------> 0 ----> resolved address

                      /---> 1 ---> S ---\
    	              |			|
 ---> 3 ----->  D  ---|			|---> 4 ----> Message
		      |			|
                      \---> 2 ---> R ---/


	My documentation is not clear on whether the envelope's recipient
	or the header's To: is used to deliver the message.

I hope this helps someone besides myself.  If anyone can improve on it,
please do.

-- 
--russ (nelson@clutx [.bitnet | .clarkson.edu])  Russ.Nelson@$315.268.6667
Violence never solves problems, it just changes them into more subtle problems