From: Bill Landry (billinetmsg.com)
Date: Tue Sep 18 2007 - 22:38:35 CDT

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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:
============
"As for advertising 8bit MIME with the accept_8bitmime option in Exim,
that's not something we are going to change:

http://www.exim.org/exim-html-current/doc/html/spec_html/ch14.html#SECTalomo

          This option causes Exim to send 8BITMIME in its response to an SMTP EHLO
          command, and to accept the BODY= parameter on MAIL commands. However,
          though Exim is 8-bit clean, it is not a protocol converter, and it takes no
          steps to do anything special with messages received by this route.
          Consequently, this option is turned off by default.

We are not going to make that sort of change the behavior of our service since many other
users who are relying on our current behavior would have the opposite problem :)"
============

It seems to me that it is pretty standard for MTAs to announce "250-8BITMIME", so what would the "opposite problem" be that they are referring to above? What could break if they started announcing "250-8BITMIME" with their ehlo reply?

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.

I know I can tell the milters to ignore the "Content-Transfer-Encoding" header in the signing, however, I'm wondering if there is a way to force "Content-Transfer-Encoding: 8bit" to this relay provider, as it appears they will accept 8bit, even though they don't announce it. This was confirmed using swaks and hard setting Content-Transfer-Encoding to 8bit:

 swaks -s xxx.xxx.xxx.xxx -f testexample.com \
        -t testexample.net --header="Content-Transfer-Encoding: 8bit"

Thoughts? Thanks for any feedback...!

Bill

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