I don't see where your problem is. The following script works fine for me. My box has an smpt server listening on port 25, a pop3 server on port 110, and nothing on ports 9805 and 9806. The results are as expected.

#!/usr/bin/perl -w

use strict;
use IO::Socket;

for my $port (25, 9805, 9806, 110) {
    my $skipA = 0;

    my $socketA = new IO::Socket::INET(
        PeerAddr => 'localhost',
        PeerPort => $port,
        Proto => 'tcp',
    ) or $skipA = 1;

    print "\$port: $port; \$skipA: $skipA\n";
}

__END__
$port: 25; $skipA: 0
$port: 9805; $skipA: 1
$port: 9806; $skipA: 1
$port: 110; $skipA: 0
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