=> 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