From: Mark Martinec (Mark.Martinec+postfixijs.si)
Date: Wed Sep 19 2007 - 02:44:17 CDT

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On Wednesday September 19 2007 05:38:35 Bill Landry wrote:
> I've been struggling with my relay provider trying to convince them to
> advertise 8bitmime in their ehlo exchange, however they are opposed to
> doing this. They say:

You are trying to solve a wrong problem. Even if you persuade
your ISP to pass 8bit mail, you can't persuade any possible recipient
of your mail (like all recipients of mailing lists) to do the same.

> It seems to me that it is pretty standard for MTAs to announce
> "250-8BITMIME"

It is common, but not universal nor required by standards.

> The problem I am experiencing with this is that when mail is sent via
> SquirrelMail, it is sent as "Content-Transfer-Encoding: 8bit", however, it
> appears that since the relay service is not announcing 8BITMIME, Postfix is
> sending the message with "Content-Transfer-Encoding: quoted-printable".
> And since the message has already been signed with both DK and DKIM, and
> the "Content-Transfer-Encoding" is included in the signing as 8bit, the
> signatures fail verification on the receiving end.

Convert to 7bit BEFORE signing your mail.

If using a content filter like amavisd, you can force Postfix
to downgrade to 7bit QP if you let amavis NOT to announce its
8-bit capability: smtpd_discard_ehlo_keywords = ('8BITMIME');
and use a signing milter AFTER content filtering. See:
  http://www.ijs.si/software/amavisd/amavisd-new-docs.html#dkim

Mark

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