File: //usr/share/webmin/postfix/help/smtpd_restrictions.html
<ul>
<li><tt>reject_unknown_client:</tt> reject the request if the client hostname is unknown.
<li><tt>permit_mynetworks:</tt> permit if the client address matches
<a href=opt_mynetworks><tt>$mynetworks</tt></a>.
<li><tt>check_client_access maptype:mapname:</tt> look up client name,
parent domains, client address, or networks obtained by stripping
octets. Reject if result is REJECT or "[45]xx text".
Permit otherwise.
<li><tt>reject_maps_rbl:</tt> reject if the client is listed under
<a href=opt_maps_rbl_domains><tt>$maps_rbl_domains</tt></a>.
<li><tt>reject:</tt> reject the request. Place this at the end of a restriction.
<li><tt>permit:</tt> permit the request. Place this at the end of a restriction.
</ul>