I received the "forward this to everyone you know" spam, delivered directly from a Yahoo! server:
Received: from web53702.mail.yahoo.com ([206.190.37.23])
by mail.spsu.edu with smtp (Exim 4.43)
id 1FU2ni-0000yx-Uj
for bMbUrNoGwEnD@spsu.edu; Thu, 13 Apr 2006 10:28:04 -0400
I sent the entire email, including headers, as shown in the "evidence" link below, to abuse@yahoo.com. Yahoo! responded with "Yahoo is in no way associated with the email you received." You mean, other than delivering it from your own server? Pathetic!
Conclusion: Yahoo is not interested in stopping spam from their own servers. Corollary: You should refuse mail from Yahoo's servers.
Evidence: the original spam email and Yahoo's response.
(My own email address above and in the 'evidence' links has been munged to prevent other spammers from harvesting it from these pages. You can un-munge it by inspection; just remove MUNGED. Complete contact information for me is here: contact.html).