<header>Restrictions on sends in HELO commands</header>
<center><tt>smtpd_helo_restrictions</tt></center>
<hr>
This parameter specifies optional restrictions on what SMTP clients can send in
SMTP HELO and EHLO commands.
<p>
The default is to permit everything. The following restrictions
are available:
<ul>
<li> <tt>permit_mynetworks:</tt> permit if the client address matches
<a href=opt_mynetworks><tt>$mynetworks</tt></a>.
<li> <tt>reject_unknown_client:</tt> reject the request if the client hostname is unknown.
<li> <tt>reject_maps_rbl:</tt> reject if the client is listed under
<a href=opt_maps_rbl_domains><tt>$maps_rbl_domains</tt></a>.
<li> <tt>reject_invalid_hostname:</tt> reject HELO hostname with bad syntax.
<li> <tt>reject_unknown_hostname:</tt> reject HELO hostname without DNS A or MX record.
<li> <tt>reject_non_fqdn_hostname:</tt> reject HELO hostname that is not in FQDN form
<li> <tt>check_helo_access maptype:mapname:</tt> look up HELO hostname or parent domains.
Reject if result is REJECT or "[45]xx text".
Permit otherwise.
<li> <tt>check_client_access maptype:mapname:</tt> see
<a href=opt_smtpd_client_restrictions>smtpd_client_restrictions</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>
Restrictions are applied in the order as specified; the first
restriction that matches wins.
<p>
Specify a list of restrictions, separated by commas and/or whitespace.
Continue long lines by starting the next line with whitespace.
<hr>
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