Today Return Path releases a new Email Deliverability Benchmark Report. It’s been a few years since we published this kind of data and the big news is that the news hasn’t changed much in that time. On average, commercial email is still being blocked at a rate of about 20%.
Want to download the report but do not want to register on Return Pah, please down load it here.
for details, please visit 2009 Deliverability Benchmark Report: Don’t Be a Statistic

EmailAddressValidator Class is a PHP class for validating email addresses according to the official specifications, and here is the Source Code. maybe I will use it in my PHP version Auto-Responder bases on Gmail(Google Apps) one day.

Today I found some one ask how to implement Yahoo DomainKeys on MS Exchange 2003, and I told him to find answer from her
https://mmmservices.web.cern.ch/mmmservices/Antispam/DomainKeysLibrary.aspx

CERN DomainKeys Library is written in C#, for a Windows usage.
Common task is to integrate this library into Protocol Event Sinks, implementing ISmtpInCommandSink interface, for incoming traffic verification and outgoing traffic signing.
An ISmtpServerResponseSink Sink might also be used for signing outgoing traffic.
It uses a certificate generated by OpenSSL, and imported in LocalMachine certificate store. The public key is extracted using OpenSSL for DNS field.

if you want solution for other smtp server, please follow this link,
http://domainkeys.sourceforge.net/

P.S.
a little knowledge about Yahoo DomainKeys

Introduced by Yahoo! Inc., the idea is to sign and verify mails at gateway level, using a public key found in DNS for verification.
The idea is to verify that the mail really comes from the official server handling this email address, to be sure it is not a forged email.

See http://antispam.yahoo.com/domainkeys for details and specification.