Configuring Sendmail to Relay Messages to Another Server

Index

Part 1. Configuring Sendmail on Solaris 10
Part 2. Configuring Sendmail to Masquerade Your Messages
Part 3. Configuring Sendmail to Relay Messages to Another Server
Part 4. Configuring Sendmail to Relay Messages from Other Servers

Introduction

Sometimes you just need to configure your Sendmail to relay messages to another server. I often use such a configuration to centralize Sendmail configuration: if something had to change I would just need to change a reduced number of configuration files. For example, I made heavy use of Solaris Zones technology. Unless particular configuration is needed, whenever I create a new zone, I just configure its Sendmail to relay messages to another server (which is, incidentally, one of the preconfigured Sendmail zones we use).

Setting Up a Sendmail Smart Host

Setting up Sendmail to relay messages to another server is pretty easy. Modify your configuration file and use the following macro:

[...snip...]
define(`SMART_HOST', `your-smart-host')
[...snip...]

The smart host is the host this instance will relay messages to. This macro will be translated into a DS statement in your Sendmail configuration file. You should never modify .cf files directly: always compile .mc files! By the way, sometimes is useful to know .cf syntax if you need to interpret existing .cf files when you've lost the corresponding .mc files (something that should never pass to a seasoned System Administrator).