Negotiated noncompliance

[John Gardiner Myers <[e-mail]>]

I propose the following additional wording for resolving the "naked LF"
issue:

Section 2.3.7, in "Conforming implementations MUST NOT recognize or
generate any other..." remove "recognize or".

Add:

6.4 Negotiated Noncompliance

A general protocol implementation principle may be useful to
implementations which wish to interoperate with particular types of
noncompliant peers: If an implementation receives protocol which is not
permitted by the specification and the specification does not mandate
the response to such illegal protocol, the implementation MAY consider
the peer to have negotiated a nonstandard protocol.  At that point, the
implementation is not constrained by the protocol specification in its
handling of that particular connection.

For example, if an SMTP server receives commands terminated by the ASCII
character "LF" but not containing the ASCII character "CR", it MAY
consider the SMTP client as having 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
variant.