[RndTbl] weird DKIM fail

[Trevor Cordes]

We're sending email on behalf of other companies with the From: (company)
and Sender: (us) set properly.  We have DKIM (domainkeys) setup with
opendkim for outgoing mail.  We have the TXT record setup properly.

This setup works for all of our customers.  Except one, and only (so far
as we know) with yahoomail.  Same setup for every outgoing email, every
company, same everything.  But just these emails just to yahoomail show a
DK fail.  All other emails for the other companies to any mail provider
show a DK pass.

I checked that the customer domain doesn't have a conflicting DK setup,
and they don't.

I'm really baffled.  Makes no sense at all.  Anyone have any ideas?