Re: [exim-dev] [Bug 1684] Malformed headers which exceed len…

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Autor: Heiko Schlittermann
Datum:  
To: exim-dev
Betreff: Re: [exim-dev] [Bug 1684] Malformed headers which exceed length spec willingly passed to remote servers
Viktor Dukhovni <viktor1dane@???> (Mi 30 Sep 2015 23:10:08 CEST):
...
> All lines over 998 bytes, whether header or body. The SMTP protocol
> requires all lines to be under 1000 bytes include the CRLF, so all
> lines are folded by default.
>
> > Or did I get somethow wrong?
> > Because I wouldn't expect to get my my plain text non-mime body lines
> > folded in any way. But I could accept a server rejecting my message
> > because of overlong physical body lines.
>
> In most cases, better folded, than dropped.


I didn't say "drop", but "reject".

> The original message
> should have used QuotedPrintable or Base64 to avoid the problem.
> Messages that emit raw output with lines longer than 1000 bytes
> are handled on a best-effort basis.


What is about the DKIM signatures in such cases? Do the signatures
tolerate such changes?

> Discovering that the message contains such lines and then automatically,
> enabling a MIME downgrade to QuotedPrintable or Base64 is possible,
> but complicated by the possibility that the message might in fact
> be QP encoded, and still have overly long lines, ...


Again, what about DKIM here? IMHO a MTA never ever is allowed to touch
the body. If the MTA doesn't want to transport message (because of
violations of the standards), it should reject the message reception.

> The Postfix approach is to prioritize delivery of mail over being
> pedantic about RFC requirements.
> This has the advantage that mail delivered locally can be accepted
> and delivered unmangled regardless of line length, only mail relayed
> out via SMTP is subject to folding.


I do not agree. Much trouble we have here is explaining people, that
there are some standards and that their mails have to follow that
standards. (Starting with mistyped addresses that people want to have
delivered anyway, continued with broken headers, long message body
lines, …) Most other parts of our life do not tolerate violating some
rules. Why mail should?

    Best regards from Dresden/Germany
    Viele Grüße aus Dresden
    Heiko Schlittermann
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