4 Setting it up in Debian

First, install postfix. This will prompt you to remove packages related to exim4. That’s okay, do it. The installation will prompt you to specify what the server is for. This step helps to configure most of the default settings.

• No configuration.
• Internet Site. This is intended for an SMTP server that is a standalone server that receives messages from other Internet SMTP servers, and it also sends messages directly to other SMTP servers.
• Internet with smarthost. This is intended for an SMTP server that has a “smarthost” capable ISP. Such a server receives Internet incoming messages from port 25, as well as outgoing messages from “inside” the organization from port 25. However, message going out of the site are sent by port 587 of ISP server. Most residential ISPs do not support smarthosts.
• Satellite system. This is intended for an SMTP server that forwards outgoing messages to a relay SMTP server, but the SMTP server accepts incoming port 25 connections to deliver messages to accounts on the server. Note that the relay SMTP server must, for one reason or another, accept port 25 connections from a satellite SMTP server. This is the most common configuration type for smaller domains that are not recognized as authoritative.
• Local only. This is intended for an SMTP server that does not have to handle SMTP connections any other hosts (to receive or send messages). In this configuration, the server is only useful for delivering messages amongst accounts on the server machine itself.