File: //usr/share/webmin/postfix/help/opt_best_mx_transport.html
<header>Action when listed as best MX host</header>
<center><tt>best_mx_transport</tt></center>
<hr>
This parameter controls what happens when the local system is listed as the
best MX host for a destination. By default, Postfix reports a "mail loops
back to myself" error and bounces the message.
<p>
Specify <tt>local</tt> to pass the mail to the local delivery agent. You can
specify any transport that is defined in Postfix <tt>master.cf</tt> file.
<hr>