List - Sender Policy Framework (SPF) protects against address forgery and makes it easier to identify sending mail servers. It 'breaks' standard email in two ways - detailed on the site -- spf.pobox.com.
Also, www.spamproxy.de has a windows version that supports SPF and MS CallerID. The implementation appears to require changes in DNS and a script in postfix. Gregory Wood Farsight Voice Data Solutions 1219 W University Blvd. Odessa TX 79764 Voice: 432-335-0879 x234
BEGIN:VCARD VERSION:2.1 N:Wood;Gregory FN:Wood, Gregory NICKNAME:ChaosID:0234342934 ORG:Farsight Voice Data Solutions TITLE:Owner ADR;WORK:;;1219 W University Blvd.;Odessa;Texas;79764-7119;USA LABEL;WORK;ENCODING=QUOTED-PRINTABLE:1219 W University Blvd.=0D=0AOdessa, Texas 79764-7119=0D=0AUSA ADR;HOME;ENCODING=QUOTED-PRINTABLE:;;=0D=0A LABEL;HOME;ENCODING=QUOTED-PRINTABLE:=0D=0A EMAIL;PREF;INTERNET:[EMAIL PROTECTED] REV:20030818T135319Z END:VCARD