How do I run multiple DNS checks in parallel with scoring?

md_async_run_checks fires all checks concurrently and blocks until every one completes or the global_timeout fires. Use md_async_score_results to tally the interpreted results into a weighted spam score and get a single PASS / REJECT / TEMPFAIL decision. This belongs in filter_begin.

use Mail::MIMEDefang::Async;
use Mail::MIMEDefang::Async::Checks qw(
    md_async_check_dnsbl
    md_async_check_rdns
    md_async_check_spf_record
    md_async_check_dmarc_record
    md_async_check_mx_exists
);
use Mail::MIMEDefang::Async::Results qw(
    md_async_interpret_dnsbl
    md_async_interpret_rdns
    md_async_interpret_spf_txt
    md_async_interpret_dmarc
    md_async_score_results
);

sub filter_begin {
    my($entity) = @_;

    my $from_domain = $sender;
    $from_domain =~ s/^.*\@//;

    # All checks fire at once; wall-clock cost = slowest single check
    my $result = md_async_run_checks([
        md_async_check_dnsbl(name => 'zen',
            ip => $RelayAddr, zone => 'zen.spamhaus.org'),
        md_async_check_dnsbl(name => 'spamcop',
            ip => $RelayAddr, zone => 'bl.spamcop.net'),
        md_async_check_rdns(ip => $RelayAddr),
        md_async_check_spf_record(domain => $from_domain),
        md_async_check_dmarc_record(domain => $from_domain),
        md_async_check_mx_exists(domain => $from_domain),
    ]);

    my %interp = (
        zen     => md_async_interpret_dnsbl(
            records => $result->{results}{zen},
            zone    => 'zen.spamhaus.org',
            error   => $result->{errors}{zen}),
        spamcop => md_async_interpret_dnsbl(
            records => $result->{results}{spamcop},
            zone    => 'bl.spamcop.net',
            error   => $result->{errors}{spamcop}),
        rdns    => md_async_interpret_rdns(
            records => $result->{results}{rdns},
            error   => $result->{errors}{rdns},
            ip      => $RelayAddr),
        spf     => md_async_interpret_spf_txt(
            records => $result->{results}{spf},
            error   => $result->{errors}{spf},
            domain  => $from_domain),
        dmarc   => md_async_interpret_dmarc(
            $result->{results}{dmarc}),
    );

    my $score = md_async_score_results(
        interpreted => \%interp,
        reject_at   => 5.0,
        tempfail_at => 12.0,
    );

    md_syslog('Info',
        "Async batch score=$score->{score} action=$score->{action} "
        . "reasons=" . join(', ', @{$score->{reasons}}));

    if ($score->{action} eq 'REJECT') {
        return action_bounce("550 5.7.1 $score->{reasons}[0]");
    }
    if ($score->{action} eq 'TEMPFAIL') {
        return action_tempfail("451 4.7.1 Temporary check failure");
    }
}