Mails are not sent to some addresses.
The following error can be found in mail log:
09/12/13 13:18:16 ME-I0009: [09542A9613144EE695DD7835AC43FDD8.MAI] Remote server has closed connection after 0 milliseconds. Server Response: (-) 09/12/13 13:18:16 ME-E0059: [09542A9613144EE695DD7835AC43FDD8.MAI] Message Delivery Failure. Attempt (23): Domain (yahoo.com) returned temporary error for email. Message has been requeued. 09/12/13 13:18:16 ME-IXXXX: [0A9BDE4490704C08A66604721DC0C96B.MAI] Remote server returned a response indicating a temporary failure. Server Response: (450 4.7.1 Client host rejected: cannot find your reverse hostname, [184.108.40.206]**)
There is no reverse DNS zone for the server IP address.
Create reverse DNS zone for the server IP address.