And then what? What would you have my receiver do differently just
because some random third party inserted a signature?
If it's a third party with a good reputation, accept and deliver the
mail, of course. If it's a third party with no reputation, you ignore
the signature, the same as a no reputation first party signature.
For example, I expect that at some point our list owner will arrange
for mipassoc.org to sign the mail from this list, mutated subject
lines and all.
Since mipassoc.org has never sent me any bad mail, and I know how to
contact him if there's a problem, what practical benefit would there
be to anyone from not delivering the mail his MTA signs and sends me?
NOTE WELL: This list operates according to