Configuring qpsmtpd is simple. As a result of its history as a replacement for qpmail-smtpd the qpsmtpd uses a similar configuration model to qmail (and will even look for and respect the contents of existing qmail configuration files).

An incomplete list of qpsmtpd configuration files.

A brief discussion of qpsmtpd environment variables.

How to support SMTPS, i.e. SMTP over SSL, using stunnel.

There is also some information if you want to run a second instance as a submission server (i.e. on port 587).