Path: utzoo!attcan!uunet!husc6!bloom-beacon!apple!bionet!agate!ucbvax!TWG.COM!dcrocker
From: dcrocker@TWG.COM (Dave Crocker)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  Food for thought
Message-ID: <8811242359.AA16614@ucbvax.Berkeley.EDU>
Date: 21 Nov 88 16:22:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 32

This is to elaborate on David Herron's reply, about MMDF.

The philosophical differences between sendmail and MMDF have always been
quite basic.  sendmail puts essentially full address parsing and mapping
decisions into the hands of the system administrator.  MMDF builds the
rules into code and gives the administrator access to certain parameterized
choices.  While the latter would seem to be simpler for administrators, the
presence of the domain system, as a logical indirection to the routing
information, makes the actual practise more painful that one would like.

In any event, when a message comes in, from ANYWHERE, address specifications
are mapped to a single canonical representation.  The works because,
ultimately, addresses reduce to a routing sequence.  That is, most of the
brouhaha about addresses has to do with syntax.  The range of semantic
choices seems to be rather small.

When the message is being sent, the channel doing the sending knows how to
map from canonical to channel-specific format.  This is built into the code.

To anticipate a concern:  You might fear that this makes MMDF too rigid in
its address handling.  To some extent, this is correct.  And intentional.

In reality, it is not very often that a new mapping algorithm needs to be
invented.  On the other hand, configuration files need to be built quite
frequently.  The world is quite sensitive to incorrect mappings and it is
not always easy to specify the mapping -- Eric Allman's efforts with
developing a language for it, in sendmail, were quite impressive -- and,
sure enough, random folk like system administrators, get it wrong frequently.

Hence the decision to bury as much of this thought into rigid code.

Dave