🚀 go-pugleaf

The pre-defined role of rulesets is as follows:

0       determine mailer for delivery. returns: <mailer,host,mailbox>
1       sender rewriting
2       recipient rewriting
3       canonicalization
4       externalization

with IDA, one has separate envelope/header rewriting, i.e.

5       sender rewriting (headers, #1 is for envelope in such systems)
6       recipient rewriting (headers, #2 is for envelopes).

Now, what happens when you ask sendmail to deliver a mesage is roughly the
following:

recipient -> canonicalize -> find_mailer -> $# mailer $@ host $: mailbox
	 	#3		 #0
		|
		+--> #2 (or #6) -> recipient'

The mailbox is transformed as

mailbox -> recipient rw. -> mailer-specific -> externalize -> mailbox'
	     #2		    rewriting rule       #4

Mail is then delivered to |mailbox'| on |host|, using |mailer| (and also
its interpretation of |host| and |mailbox|). The To: header field will
contain |recipient'|.

Similar transformations are done with the sender field but there is no call
to ruleset #0:

sender -> canon. -> sender rw. -> mailer-specific -> externalize -> sender'
	    |			  rewriting rule
	    |
	    +--> sender rw. (#1 or #5) -> sender"

Now, what you will see is:

Message Header - 	From: sender"
			To: recipient'

Message Envelope -	RCPT To: mailbox'
			MAIL From: sender'
	while talking SMTP to "host".

Of course, with other mailers, the dialogue looks a little different, but
basically the envelope/header structure remains the same.

[I hope I've got all these arrows right.]

-- 
Juergen Wagner		   			gandalf@csli.stanford.edu
						 wagner@arisia.xerox.com