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The main server cluster sits on the back end of our mail delivery system and runs a commercial high capacity mail system. We currently offer POP (Post Office Protocol) mail boxes for our users and domain mail hosting. Access to the back end mail cluster is permitted only to authenticated users. Authenticated users are users that have a valid username/password on the mail cluster. All other SMTP (Simple Mail Transfer Protocol) traffic through the firewall is diverted to our front line clusters. Access to the back end cluster is also made directly when you POP your email by using a client like Outlook, or when you access the web based email. As with SMTP access to this cluster for these services require a valid username and password.

Another main function of the mail cluster is the SPAM engine. This is the place where most of the SPAM checking is done and the headers are tagged with special phrases to indicate that the mail may potentially be SPAM.

All inbound mail for any domain is directed to a server by using a special record in the domains DNS called an MX record. Your domain can have multiple MX records directing mail to multiple servers and they can be ordered by priority. At LHH we use two small inbound clusters, MX1 and MX2 each of which accept only inbound mail from our network and the internet. The purpose of these inbound mail servers is to accept inbound mail for our customers only. They do this by validating the incoming mail to make sure the domain it's addressed to is on our primary back end mail server. If it is not the mail is rejected and the sender gets the familiar "Relay Not Permitted" which prevents unauthorized individuals from sending mail (SPAM) through our servers. These inbound servers have several functions:

• They perform "Sender Verification" checks in which they actually contact the sending mail server to check the sender's address. If the senders address is not valid, the mail is rejected. This prevents SPAMMERS from sending mail from non-existent accounts.
• They perform "Recipient Verification" checks in which they check the destination mail box to make sure the mail box exists on our server before the mail is sent. This eliminates a huge volume of mail traffic from our network. SPAMMERS will often send out a thousand messages to a single domain trying all standard names for mail boxes and typically succeed with hitting some legitimate mail accounts.
• They perform Anti-Virus checks. All inbound mail is checked against a live database from a commercial provider. The Anti virus signatures are updated every 5 minutes. If an inbound virus or registered scam email is detected, the email is immediately dropped from our systems.
• They perform inbound header checks. Email headers are very informative and precise. It is fairly easy to forge these headers and enter false information in an attempt to hide the true identity of the sending party or server. These inbound servers perform over 10 checks on the header to try to identify forged headers and remove them from the mail stream before they are delivered.
• They perform inbound DNS Black List Checks and Reverse DNS checks. If the inbound mail is found on any one of six high end black lists the header is tagged. Another important requirement for proper mail delivery is the ability of the receiving mail server to identify the sending mail server by it's name by looking up it's name in the DNS using the sending IP address. This is known as Reverse DNS. All mail systems must be able to be resolved using reverse DNS. Mail servers used specifically for spamming and illegal activities typically do not have a reverse DNS. If there is no reverse DNS, the headers are tagged.

One last functional feature of the inbound mail systems is the ability to provide load balancing, redundancy, and mail queuing. Our customers all have multiple MX records all with the same preference level. This means that at any given time a mail server trying to send mail to a customer hosted on our service might get any one of the two inbound clusters. This random selection process provides load balancing for our inbound mail eliminating delivery delays. It also provides for redundancy. By design if a mail server contacts another mail server and that mail server is down, usually the mail is held by the sending mail server and retried at some interval until it either gives up or can deliver the mail. In our case if the sending mail server cannot reach one of our clusters, it will pick up another MX record and try that cluster and the mail will be delivered. this provides fail over protection for our mail system.

Lastly, because our receiving servers are redundant and separate from our main cluster, If we need to take the main cluster off line for some reason or we are having hardware problems with the main mail systems, you mail will continue to be accepted by our network and queued. Within two minutes after the primary mail server becomes available again, your mail will be delivered.

The outbound mail clusters provide almost the same service as the inbound clusters do with a few exceptions. We do not perform DNS Black list checks or reverse DNS checks on outbound mail because the only outbound mail we accept must ultimately originate from our back end mail systems. We do perform anti-virus checks to ensure that our own customers are not sending viruses through the mail and we also perform anti-SPAM checking, different from that of our inbound servers. The outbound servers are specifically looking for SPAM that may be originating from one of our own mail customers.

The biggest difference in the outbound servers is their ability to offload the SMTP (mail sending processes) from the primary back end mail servers. In past configurations mail delivery delays may have been experienced if the mail cluster was extremely busy sending out mail or processing a very large mailing list. This no longer happens because all the outbound mail is offloaded to the outbound relay clusters which are load balanced and high capacity server able to handle the single task of sending out the mail rather than needing to be concerned with the other mail functions.