Example Setup

The examples in this guide will use a real-life setup detailed below. The setup being used will have a main SMTP server which will act as a mail relay to a mailbox/spool server that stores the mail.

The following diagram outlines this configuration:

We will be using the 192.168.50.0/24 network (corp.guardiandigital.com) for our example. The two mail servers will be:

192.168.50.2 (smtp.corp.guardiandigital.com)
192.168.50.3 (mailbox.corp.guardiandigital.com)

Generally these two mail servers will be located on the same network, protected by a firewall. DNS service will be required. However, both the configuration of a firewall and DNS is beyond the scope of this guide.

Here, smtp.corp.guardiandigital.com is the SMTP server that receives mail from the Internet. mailbox.corp.guardiandigital.com is the mail store.
smtp.corp.guardiandigital.com receives mail for the domain corp.guardiandigital.com, and forwards it to mailbox.corp.guardiandigital.com. mailbox.corp.guardiandigital.com stores mail for the domain corp.guardiandigital.com, and local users access it to read their mail. All local user accounts exist in mailbox.corp.guardiandigital.com.

You can create just one server to be a mail store without involving a relay. This means that the mail store must be able to receive mail directly from the Internet. Follow the instructions for creating a mailstore, but leave the relay host and backup relay host empty.