ISP signatures on outgoing mail

[nobody@REPLAY.COM (Anonymous)]

Anyone heard of a proposal for ISPs to automatically sign outgoing
mail headers?  Problem has been that spammers send email by one
path but forge a reply-to or from address at another location.  Most
recent case is hotmail, which got blocked by netcom over a spam attack.
Actually mail didn't come from hotmail, was forged to look like it came
from there.  Same thing has happened to remailers.

They need a standard for which headers to sign, then a dig sig can be
included in the headers to check that a message came from where it
claims.