It’s not clear that this has anything at all to do with your DKIM signing.  The error returned by Yahoo’s mail server is too generic to tell why it got rejected.


From: Tony Birnseth, 1st Source IT, LLC []
Sent: Tuesday, August 25, 2009 8:46 PM
To: dkim-milter general discussion
Subject: [dkim-milter-discuss] Can anyone explain this?


I sent a batch of emails today as part of a marketing campaign.  I received several ND responses similar to this one and was wondering if there is a way for me to determine the cause (real addressee xxx'd out).

This is the mail system at host
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to <postmaster>
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
                   The mail system
<>: host[] said: 554
    5.7.1 Command rejected (in reply to end of DATA command)

Reporting-MTA: dns;
X-Postfix-Queue-ID: 32B4E2D283E1
X-Postfix-Sender: rfc822;
Arrival-Date: Tue, 25 Aug 2009 14:10:35 -0700 (PDT)
Final-Recipient: rfc822;
Original-Recipient: rfc822;
Action: failed
Status: 5.7.1
Remote-MTA: dns;
Diagnostic-Code: smtp; 554 5.7.1 Command rejected