I am writing this blog post to address the issue of ExchangeDefender mail receipt delays or mail simply not arriving at all. Nearly three weeks after we have implemented the new networks, and nearly a month after we have notified all our ExchangeDefender customer administrators we are still fighting with the ad-hoc issues related to delayed mail, mail that was not received, mail that was received hours later.

In 100% of the cases the issue was the recipient policy on the target mail server. Please, please, please make sure you have added the following IP address blocks in order to allow our new servers to relay mail to you:

64.182.140.0/24

64.182.139.0/24

If you do not allow those IP address ranges access to your network the system will not bounce the messages. Instead, our intelligent routing system will route messages internally to the server that is able to establish a connection with you. This system, however, was not designed to handle sysadmin apathy but instead to respond to major interruptions in the Internet backbone. If a system is unable to deliver the message directly to the server it reattempts every 15 minutes. After the first hour it sends a broadcast message asking other networks to see if they can establish a route and receive the SMTP banner. If the connection can be established the message is routed to that server and then delivered. By not having the proper IP address restrictions in place you are forcing your inbound mail to be put through our DR scenario which is automatic but time consuming.

Please, either do not use IP restrictions at all or update them properly. For a little more positive note, tune in later tonight when we’ll announce our new email SPAM reports.