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Re: 2822upd-04 line length limits

2008-01-27 13:40:21

Bruce Lilly wrote:
No!  The MIME RFCs specifically state that lines (in header or body)
which use MIME encoding are limited to 76 (N.B. not 78 or 998) characters.
Please do not suggest, imply, or leave to the reader's imagination that
MIME-encoded text can be placed in long lines. Do not under any
circumstances imply that MIME-conforming implementations must handle
encoded text in lines "at least up to the 998 character limit".

Section 2.3 states in part (I'll address the other part in a separate message):

   o  Lines of characters in the body MUST be limited to 998 characters,
      and SHOULD be limited to 78 characters, excluding the CRLF.

      Note: As was stated earlier, there are other documents,
      specifically the MIME documents ([RFC2045], [RFC2046], [RFC2049],
      [RFC4288], [RFC4289]), that extend this specification to allow for
      different sorts of message bodies.  Again, these mechanisms are
      beyond the scope of this document.

Note (as stated above) that the MIME RFCs *limit* line lengths to 76
characters when MIME encoding is used.  The text "extend this specification"
might be misinterpreted (76 characters is a *limitation*, not an
*extension*) w.r.t. line length limits.  At a minimum, some clarification
of this point is needed in the draft text.


you are both correct and incorrect. The MIME specifications cover a number of transfer encodings. Two of those (quoted-printable and base64) limit the lines to 76 characters plus a CRLF, as you describe.

Two of the MIME encodings (7bit and 8bit) retain the 998 line limit. (RFC 2045 sections 2.7 & 2.8)

However, one of the MIME encodings (binary) REMOVES all line length limitations. (RFC 2045 section 2.9) It does indeed *extend* the specification.

And there is room left within the specification for other encodings to be defined that have other limitations, although none are currently defined within the MIME specs, nor is it likely that there ever will be any.

I suggest changing the wording "extend this specification" to be "shorten or extend this line length limitation".

        Tony Hansen

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