We all dislike spam, virus infected emails and other nasties finding their way into our inbox! For this reason we spent several months designing, testing and implementing a system to bring this problem to an absolute minimum with great success.
Our MailGuard Email Cluster is enabled as standard on all shared/reseller web hosting packages and is a cluster of machines taking different roles in the process of accepting incoming email for all hosted domains. With powerful features such as detailed spam detection, Optical Character Recognition, RFC compliancy, sensible greylisting, quarantined email and much more, it cannot be beaten for features or accuracy (we have tested against some third party 'solutions').
MX servers
At the time or writing we have two independant MX servers with all incoming email arriving to one of them during the first stage of delivery (equal priority MX records). These servers will first run a series of checks on the sending server to ensure that appropriate RFC guidelines are followed and that the sending server is not on any accurate spam blacklists. If these tests fail the connection is denied with more severe blocking put in place for large amounts of failures from the same sender (dictionary attack).
Content Filters
When an email is accepted at one of our MX servers it is then passed to one of the CF machines (currently 3 in operation). These servers are very powerful and take the role of scanning emails for any virus infection (definitions updated every 15 minutes) and assigning a spam score. The spam checking involves several thousand individual tests including common phrases, OCR, PDF scanning and many more with each test having a score attached to it.
After an email is scanned, if deemed as clean/non-spam it is then passed back to the MX server where it will then be added to the user inbox. However, if deemed to be spam or bad in some way (virus, etc) it will be quarantined which allows all clients to check email caught as spam before confirming whether this is correct or wrong.
Frontend
All settings for our email system can be controlled on a 'per domain' basis via our cPanel® control panel. This allows clients to enable/disable any aspect of the scanning, set custom spam scores along with the action for spam email. If quarantines are enabled (as default) all clients can view their list of quarantined email and assist in the auto learning process by confirming or correcting the results of the scanning.
Failover
A huge benefit of the above system is the expandability and redundant nature. Due to each task being handled separately if more capacity is required it is simply a case of adding more machines for that task. If any particular machine should develop a fault, it is automatically removed from the cluster with everything handled by other machines responsible for that task.
As an additional step of redundancy, we have one final element in the cluster to act as a complete failover. In the event of a critical problem such as network issue whereby both front line MX servers are unavailable, our failover servers (hosted off network) will take over and accept the incoming email. This email will be queued then forwarded to the MX servers when they become available again. While this can result in a delay to email in the event of critical network issues, this is more favourable than it's alternative where email is lost completely.
Other hosting features...
