Re: Negotiated noncompliance

Eliot Lear <> Wed, 23 August 2000 11:51 UTC

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Date: Wed, 23 Aug 2000 04:28:26 -0700
From: Eliot Lear <>
Organization: Cisco Systems
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CC: John Gardiner Myers <>
Subject: Re: Negotiated noncompliance
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I would like to separate two issues: wording of section 6.4 and whether
we strike "recognize" in section 2.3.7.

In reverse order, I believe we are at or near consensus on Chris'
wording, taking into account John's and Philip's changes.  Do others

6.4 Interoperability with Noncompliant Implementations

This standard takes a stricter tone than its predecessor in order to 
discourage deployment of non-complaint software and to prevent harm
by poorly designed attempts to interoperate with deployed non-compliant 
software.  It does so with the experience of nearly twenty years of odd 
interoperability failures, and with the realization that whereas
of people used SMTP at the time of RFC 821, now millions of people rely
the standard.  Non-conformance, therefore, can be far more costly.

If an implementation receives protocol which is not permitted by the 
specification and the specification does not mandate the response to
illegal protocol, the implementation can treat this as a negotiated a 
non-standard protocol.  At that point, the implementation is not 
constrained by the protocol specification in its handling of that 
particular connection.  Implementations which choose to do this SHOULD 
narrowly tailor the accepted non-compliant protocol to that strictly 
necessary to interoperate with known deployed non-compliant software.

For example, if an SMTP server receives commands terminated by the ASCII
character "LF" but not containing the ASCII character "CR", it can
the SMTP client has negotiated a nonstandard variant of
the SMTP protocol wherein the <CRLF> sequence is encoded as a single
"LF" character.  The prohibition against recognizing the sequence
"<LF>.<LF>" as the end of mail data indication would then not apply to
that particular connection.

Note that this negotiation does not release the implementation from the
conformance requirements in any other protocol session, including any
session that relays mail received from a negotiated nonstandard protocol

We are NOT in complete agreement on what to do about section 2.3.7, but
I believe we are arguing between a MUST/SHOULD and striking the word
"recognize".  As I wrote earlier, I could survive with SHOULD, but would
still prefer MUST, and I would not wish to hold up the draft in any
event.  My argument is that 6.4 should be taken into consideration wrt
2.3.7 as it would be with other parts of the document.  The document
doesn't mandate a RESPONSE to naked LFs.  It merely states they should
not be "recognized" as <CRLF>s.

Eliot Lear