=> 0: DKIM and maillists => 1: Dejan Štrbac's blog also in: [Links/Personal] => 2: Email authentication validness check check-auth-jsmith=yourdomain.com@verifier.port25.com => 3: FengHe's blog also in: [Links/Personal] => feed => 4: Mail blacklist check => 5: Mail operators also in: [Links/Maillist] => 6: Use plaintext email