Steffen Nurpmeso via Postfix-users:
> Wietse Venema via Postfix-users wrote in
> <[email protected]>:
> |Tim Coote via Postfix-users:
> ..
> |> SMTP headers are often 'folded' as they flow through MTAs. The
> |> standard approach to folding and unfolding is covered in rfcs 5322
> ...
> |3) Lines that exceed 998 bytes (not including <CR><LF>) cannot be
> | sent in SMTP. The result of sending such text is UNDEFINED.
> ...
> | When a line is too long, the Postfix SMTP client inserts
> | <CR><LF><SPACE> (controlled by smtp_line_length_limit).
>
> This is a deficit of the entire RFC *822 series that a superficial
> whitespace is necessary at that point. It was simply not on the
> table, and i got not even an answer on that in private
> communication (but maybe because of my way of speaking things out,
> i mean, isn't that just a desaster: this *breaks* the protocol).
> (On the other hand the dinosaur nmh just got (partially) proper
> line folding in September last year:
>
>
> http://git.savannah.gnu.org/cgit/nmh.git/commit/?id=542cb12b6d0646b711772ee97c1e2aacf2bada86
>
> and they will fail for the artificial case as i said in
>
> https://lists.nongnu.org/archive/html/nmh-workers/2023-08/msg00010.html
> [https://lists.nongnu.org/archive/html/nmh-workers/2023-08/msg00011.html])
>
> | Before Postfix inserted <CR><LF><SPACE>, some MTA would insert
> | a line break after ~1024 without adding a space. This would
> | "terminate" the message header, destroy the MIME structure, and
>
> This is really what they do? Then .. my "artificial whitespace"
> thought of a decade ago would be wrong. I would have thought they
> possibly reformat with RFC 2047 (if they can), as i said in the
> msg00011 thing above.
Yes this was a real problem.
For example, an email message like this:
label: value
label: value-that exceeds-smtp-limit
...zero or more label: value...
MIME-Version-1.0
Content-type: multipart/mixed, boundary="foobar"
END_OF_PRIMARY_HEADER
This is a multi-part message in MIME format.
--foobar
first body part
--foobar
first body part
--foobar--
Was received as:
label: value
label: value
label: first-part-of-value-that-exceeds-smtp-limit
END_OF_PRIMARY_HEADER
first body line with remainder-of-value-that-exceeds-smtp-limit
>From here on all remaining content including headers and MIME
boundaries was received as one large non-MIME message body and was
displayed to the user in its encoded form includeing MIME boundaries
encoded text (quoted-printable or base62 encoded).
Why did that happen? Because some MTA's input reader did not know
if it was reading a header or body line.
Wietse
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