Re: DMARC: perspectives from a listadmin of large open-source lists

["John R. Levine" <[e-mail]>]

>want to allow modification of the subject field (e.g., adding a tag)
>and/or the body (e.g., adding header and footer) - then you might have
>to be a little cleverer, perhaps by providing information about the
>diffs in extra headers and doing a few comparisons at the receiving end
>(subject tag = *****<original-signed-subject>).

That's unlikely to be a productive direction to go.  We had a lot of 
arguments about message modification when we were designing the DKIM 
strict and loose message digests.  We never found a way to allow subject 
tags that wouldn't also enable all sorts of abuse, and I don't think we 
missed anything.

The reasonable way to use DKIM with mailing lists has always been for
the list to add its own signature, and to use the list signatures to
develop a (presumably good) reputation for the list so its mail gets
delivered.  See the signatures on the messages from this list for an
example.

R's,
John