JumpStart II: Configuring sendmail on a Server

If you want to receive inbound email sent to a registered domain that you own, you need to set up sendmail as an incoming mail server. This JumpStart describes how to set up such a server. This server

Accepts outbound email from the local system only.
Delivers outbound email directly to the recipient's system, without using a relay.
Accepts inbound email from any system.

This server does not relay outbound email originating on other systems. Refer to "access: Sets Up a Relay Host" on page 638 if you want the local system to act as a relay. For this configuration to work, you must be able to make outbound connections from and receive inbound connections to port 25.

The line in sendmail.mc that limits sendmail to accepting inbound email from the local system only is

DAEMON_OPTIONS('Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

To allow sendmail to accept inbound email from other systems, remove the parameter Addr=127.0.0.1, from the preceding line:

DAEMON_OPTIONS('Port=smtp, Name=MTA')dnl

By default, sendmail does not use a remote SMTP server to relay email, so there is nothing to change to cause sendmail to send email directly to recipients' systems. (JumpStart I set up a SMART_HOST to relay email.)

Once you have restarted sendmail, it will accept mail addressed to the local system, as long as a DNS MX record (page 726) points at the local system. If you are not running a DNS server, you must ask your ISP to set up an MX record.