On 2012-05-01 18:55:20 +0300, Riku Voipio wrote:
> On Tue, May 01, 2012 at 12:48:10AM -0400, Chris Knadle wrote:
> > I think it would be useful to describe what issue(s) there are concerning
> > 8BITMIME and why this is important. I've found some information [1] about
> > this, but it isn't clear what problems are actially *caused* by the lack of
> > 8BITMIME support by default in Exim. Is it just slow sending of outbound
> > attachments?
>
> It's both extra traffic (not that much if western encodings) and extra
> cpu work. In lesser annoyance, it means that you no longer can read
> mailbox files with non-mime capable readers (for example less) with ease,
> as there will be qp encodings here and there. People who only use english
> only hit the issue when having lines longer than 76 characters.

It might also affect spam detection.

Now, the main reason I dislike Exim is

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=485751

Basically, when invoked as sendmail, Exim breaks the sendmail
compatibility by keeping the Bcc header, involving security
and/or privacy problems. And since this is by design, it won't
be fixed.

BTW, since it must accept 8-bit mail via this interface, it is
also broken as the mail may be sent to a MTA that doesn't announce
8BITMIME, since Exim doesn't know to do the conversion.

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Hello,

On Tue, 1 May 2012 23:03:38 +0200
Philipp Kern <pkern@debian.org> wrote:

> > I wonder why many people in this thread still don't understand this.
> > And also I can't see why some find this annoying behaviour or
> > something wrong. There's absolutely nothing wrong with what it does
> > now, as re-encoding will happen somewhere anyway as there are still
> > many really non-8-bit-compliant MTAs, so why should Exim do this?

> Exim transmits 8bit mails to non-8bit-compliant MTAs, so what exactly
> are you arguing?

No it doesn't if 8BITMIME annouces are turned off!

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On Tue, May 01, 2012 at 08:18:07PM +0200, Philipp Kern wrote:
> So just stop Postfix doing the conversion?

It's not just postfix, it's at least courier and sendmail and various
propiertary MTA's do conversions when encountering default configured
exims.

It would be a RFC violation to just pass 8bit mails to servers not
advertizing 8bitmime. It would be rfc compatible to the sending server
to bounce instead of qp-converting 8bit mails, but that would arguably
be even worse.

> Or teach Exim to announce 8BITMIME by default.

That would be a rfc violation as well.

Riku


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On Wed, 2 May 2012, Riku Voipio <riku.voipio@iki.fi> wrote:
> It would be a RFC violation to just pass 8bit mails to servers not
> advertizing 8bitmime. It would be rfc compatible to the sending server
> to bounce instead of qp-converting 8bit mails, but that would arguably
> be even worse.

No, bouncing mail when it can't be properly delivered is much better than
violating RFCs.

Mail that is bounced with a human readable message describing the real cause
of the problem can then be re-sent once the problem is fixed.

Having mail be silently corrupted is not acceptable.

I've spent a lot of time debugging email problems over the years...

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On Wed, May 02, 2012 at 08:44:12AM +0200, Andrew Shadura wrote:
> No it doesn't if 8BITMIME annouces are turned off!

If exim receives an 8 bit mail, even if it hadn't announced 8BITMIME in
the EHLO response, it will relay that message verbatim to other hosts.


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On Wed, May 02, 2012 at 07:05:14PM +1000, Russell Coker wrote:
> Having mail be silently corrupted is not acceptable.

Can you expand on "silently corrupted", here? Is that when you re-encode the
mail and send it on as 7-bit, or when you leave it alone and send it as 8 bit
to a host that doesn't advertise accepting 8-bit?


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On Wed, 2 May 2012, Jon Dowland <jmtd@debian.org> wrote:
> On Wed, May 02, 2012 at 07:05:14PM +1000, Russell Coker wrote:
> > Having mail be silently corrupted is not acceptable.
>
> Can you expand on "silently corrupted", here? Is that when you re-encode
> the mail and send it on as 7-bit, or when you leave it alone and send it
> as 8 bit to a host that doesn't advertise accepting 8-bit?

When you send 8 bit mail to a host that only supports 7 bit then it will be
corrupted, usually without any notification of what happened - definitely
silent corruption.

When you re-encode mail and send it on IFF the message is DKIM signed it could
be considered to be silent corruption as the change will usually count as
breakage.

It would be possible for a DKIM verification program to re-encode 7bit
messages to 8bit for a second attempt at verification. But if a DKIM milter
author was going to do tricky things then a better first option would be to
try removing anything between [] in the subject line which is the most common
cause of DKIM failures that I see on valid mail.

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On Wednesday, May 02, 2012 07:23:13 PM Russell Coker wrote:
> On Wed, 2 May 2012, Jon Dowland <jmtd@debian.org> wrote:
> > On Wed, May 02, 2012 at 07:05:14PM +1000, Russell Coker wrote:
> > > Having mail be silently corrupted is not acceptable.
> >
> > Can you expand on "silently corrupted", here? Is that when you re-encode
> > the mail and send it on as 7-bit, or when you leave it alone and send it
> > as 8 bit to a host that doesn't advertise accepting 8-bit?
>
> When you send 8 bit mail to a host that only supports 7 bit then it will be
> corrupted, usually without any notification of what happened - definitely
> silent corruption.
>
> When you re-encode mail and send it on IFF the message is DKIM signed it
> could be considered to be silent corruption as the change will usually
> count as breakage.
>
> It would be possible for a DKIM verification program to re-encode 7bit
> messages to 8bit for a second attempt at verification. But if a DKIM milter
> author was going to do tricky things then a better first option would be to
> try removing anything between [] in the subject line which is the most
> common cause of DKIM failures that I see on valid mail.

That and mailing list footers.

Receivers are, of course, free to manage inbound mail filtering however they
want, but if you take a message and try to recode it from 7 bit to 8 bit and
see if a DKIM signature passes verification, it's still not a valid DKIM
signature in any sense that RFC 4871 or its successors would recognize.

Scott K


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On Wed, 2 May 2012, Scott Kitterman <debian@kitterman.com> wrote:
> > It would be possible for a DKIM verification program to re-encode 7bit
> > messages to 8bit for a second attempt at verification. But if a DKIM
> > milter author was going to do tricky things then a better first option
> > would be to try removing anything between [] in the subject line which
> > is the most common cause of DKIM failures that I see on valid mail.
>
> That and mailing list footers.

Footers can be solved with the l= flag. The threat of a hostile party
appending data to a message probably isn't something you really worry about
when posting to a mailing list.

It would be possible for a DKIM signing program to use l= for every message
which has a recipient address containing the string "list".

> Receivers are, of course, free to manage inbound mail filtering however
> they want, but if you take a message and try to recode it from 7 bit to 8
> bit and see if a DKIM signature passes verification, it's still not a
> valid DKIM signature in any sense that RFC 4871 or its successors would
> recognize.

If a milter replaced the message body such that it matched then it would be.

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Hello,

On Wed, 2 May 2012 10:06:31 +0100
Jon Dowland <jmtd@debian.org> wrote:

> On Wed, May 02, 2012 at 08:44:12AM +0200, Andrew Shadura wrote:
> > No it doesn't if 8BITMIME annouces are turned off!

> If exim receives an 8 bit mail, even if it hadn't announced 8BITMIME
> in the EHLO response, it will relay that message verbatim to other
> hosts.

But it won't receive it at all if the sender is standards-compliant.

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