We have already established that a significant number of mailing lists
(20% +/- ???) do not supply a Sender: header. I don't think anyone
has check to see how many of the Sender: headers that are supplied
would likely be consistent with MARID validation.
We have established that one service corresponding to 10% and one
platform corresponding to 10% do not fill sender today.
Turns out that it is very easy to fix both. ezmlm just needs a
line adding to the header file - no need to re-install, just fix the
config.
Yahoo seem to be receptive to change their service if we ask
them to.
I don't think any mail forwarders supply a Sender: header.
This is an issue that is a bit trickier.