`emailrelay-check-ipaddress.pl <emailrelay-check-ipaddress.pl>`_
----------------------------------------------------------------

.. code:: perl

    #!/usr/bin/env perl
    #
    # SPDX-FileCopyrightText: 2026 Graeme Walker <graeme_walker@users.sourceforge.net>
    # SPDX-License-Identifier: FSFAP
    # 
    # Copyright (c) 2026 Graeme Walker <graeme_walker@users.sourceforge.net>
    # 
    # Copying and distribution of this file, with or without modification,
    # are permitted in any medium without royalty provided the copyright
    # notice and this notice are preserved.  This file is offered as-is,
    # without any warranty.
    # ===
    #
    # emailrelay-check-ipaddress.pl
    #
    # An example E-MailRelay filter script that verifies the
    # submitting client's IP address. The IP address is read
    # from the envelope file. Invalid IP addresses are rejected
    # by deleting the two message files and exiting with the
    # special exit code of 100. Note that this checks the IP
    # address very late in the submission process; a firewall
    # or DNSBL check might work better.
    #
    
    use strict ;
    use warnings ;
    use IO::File ;
    $SIG{__DIE__} = sub { (my $e = join(" ",@_)) =~ s/\n/ /g ; print "<<error>>\n<<error: $e>>\n" ; exit 99 } ;
    
    my %allow = (
    	"127.0.0.1" => 1 ,
    	"1.1.1.1" => 1 ,
    	# etc
    ) ;
    
    my $content = $ARGV[0] or die "usage error\n" ;
    my $envelope = $ARGV[1] or die "usage error\n" ;
    my $fh = new IO::File( $envelope ) or die "cannot open envelope file: $!\n" ;
    my $txt ;
    {
    	local $/ = undef ;
    	$txt = <$fh> ;
    }
    my ( $ip ) = ( $txt =~ m/X-MailRelay-Client: (\S*)/m ) ;
    if( $allow{$ip} )
    {
    	exit( 0 ) ;
    }
    else
    {
    	print "<<not allowed>>\n<<not allowed: $ip>>\n" ;
    	unlink( $content ) ;
    	unlink( $envelope ) ;
    	exit( 100 ) ;
    }
    

.. _../examples/emailrelay-check-ipaddress.pl: emailrelay-check-ipaddress_pl.html