This document describes how to use Virtual Gateway Technology on the Cisco Email Security Appliance (ESA).
Virtual Gateway Technology
Virtual Gateway Technology allows you to create multiple IP interfaces to have a unique hostname and mail delivery queue. The ESA will appear to be more than one server when interacting with other servers, meaning that each IP interface or IP interface group is a Virtual Gateway.
The goal of Virtual Gateway Technology is to ensure that each interface identifies itself according to the configured specification. For example, when multiple listeners are configured, each one is assigned to an IP interface. When a server connects to the listener, it will provide a banner which states the appropriate hostname associated with that IP interface. This is important if the appliance is hosting multiple domains and each domain must have its own listener and unique banner.
Virtual Gateways can be used to improve delivery. You can create a group of IP interfaces and use that Virtual Gateway to deliver messages. The ESA will rotate through the IP addresses and distribute delivery over the group of IP addresses. As each Virtual Gateway connects to a server, it provides the appropriate hostname in the HELO or EHLO SMTP command. This is advantageous when delivering high volumes of mail to systems that limit connections, messages, or recipients on a per-IP basis. This can also be used to ensure that the forward and reverse DNS match the hostname provided in the HELO or EHLO.