IP-sharing

Using the Mailtraq Cluster Gateway to run multiple domains on the same IP address

This scenario occurs when you have a single public-facing IP address, but you want to run several independent Mailtraqs, where each Mailtraq has its own domain name and set of users.

There are two issues to be aware of, although in practise they are most unlikely to cause problems:

1. The Cluster Gateway needs to present itself with a HELO string, which will be the same for all connections to it. Generally this is not a problem – you simply set it to match the domain defined in your Reverse DNS for that IP address. Just be aware that this will not always match the domain name of your mail sever.
    
2. If the Cluster Gateway receives a message for multiple recipients, where some are on one machine, and some are on another, and if the first machine rejects the message based on content (ie because it thinks it is spam) then the other machine will not receive the message, even if it would not regard the same message as being spam. In other words, if one mail server rejects it as spam, the Cluster Gateway makes the assumption that all the other mail servers in the cluster would reject it too.