Blocking "direct-from-dialup" spam is best done on the receiving end, blocking *unauthenticated* SMTP connections made directly from dial-up IPs.

If there were a definitive list of dialup and DHCP IP ranges, I might agree. But after some years of compiling the MAPS DUL, Pan Am's PDL, the osirusoft list, and who knows how many others, there isn't, so I don't see how that's a practical approach. Blocking outbound SMTP also prevents relay exploits of unsecured servers that will never be secured, and there'll never be a definitive list of them, either.

IMHO, to block ALL outbound port 25 traffic on the sending end is throwing the baby out with the bathwater.

It certainly is, but for most ISPs, there's a very small baby in a huge tub of spam. Remember that this whole question only occurs for dialup or DHCP users who are not using their ISP's mail service. While that probably includes just about everyone you and I know, overall, it's a teensy minority of ISP customers. Regards, John Levine, johnl@iecc.com, Primary Perpetrator of "The Internet for Dummies", Information Superhighwayman wanna-be, http://iecc.com/johnl, Sewer Commissioner "A book is a sneeze." - E.B. White, on the writing of Charlotte's Web