Set Up ESMTP on a Cisco Firewall

Extended Simple Mail Transport Protocol (ESMTP) enhances support for the Cisco Internetwork Operating System (IOS). When businesses can use ESMTP to install mail servers behind a firewall rather than Simple Mail Transport Protocol (SMTP). Both of these protocols establish a Transport Control Protocol (TCP) channel from server to client to exchange email. The difference is that ESMTP uses the Extended Hello (EHLO) command. This provides troubleshooting support by creating a series of extensions that allow error codes to go back to the client if a message transmission failure occurs


1.Type "enable" (without quotes) on the router to enter the privilege mode on the firewall. You enter all commands in the command line editor, which automatically starts when the router is turned on. The screen will look like this:

2.Privilege mode allows you to work only using certain configuration commands; for example, you cannot enter interface commands here. There are multiple modes on the router. Think of a mode like a floor in a building. In the higher floors, you can do certain things you could not do on lower floors.

2.Type "config t" (without quotes) in order to enter the global configuration mode. Type "ip inspect name email esmtp" (without quotes), where "email" can be any name you chose. This command configures inspection on the router. The inspection command will look at different parameters before the email transmission occurs. One extension is message size, another is the delivery status notification. In all, the router inspects eight extensions.

3. Type, "interface e0" (without quotes) to assign the inspection duties to an interface. The interface is the router's physical connection to the network. Here, it supports Ethernet.

4. Type "ip inspect email in" (without quotes) in order to apply the inspection rule to the Ethernet interface. Type "end" (without quotes) and then type "copy run start" (without quotes) to save the configuration.

Source : Ehow