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Re: switching from exim to postfix

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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