The qmail Handbook

qmail-smtpd Doesn't Automatically Relay for the Local Host

By default, qmail-smtpd doesn't accept messages for remote hosts-even if the SMTP client is a Mail User Agent (MUA) running on the local host. If you want to allow local MUAs to inject mail via SMTP, you must enable selective relaying and grant relay access to 127.0.0.1, the local host. See Chapter 3, "Configuring qmail: The Basics," for more information about selective relaying.