How can I add an Authentication-Results header?

The Authentication-Results header consolidates SPF, DKIM, DMARC, and BIMI results into a single header, making them available to downstream mail clients and filters. Add it in filter_begin so it is present before the message body is processed.

When the optional Mail::BIMI module is installed and $bimi_domain is supplied, md_authres will append a bimi=pass (or bimi=fail) result automatically.

use Mail::MIMEDefang::Authres;

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

    # Extract the From: domain for BIMI lookup (optional)
    my $from_domain = $sender;
    $from_domain =~ s/^.*\@//;

    my $authres = md_authres(
        $sender,       # envelope sender (MAIL FROM)
        $RelayAddr,    # connecting IP address
        $MyHostName,   # this server's hostname
        $Helo,         # EHLO/HELO name (optional)
        $from_domain,  # From: domain for BIMI (optional)
    );

    action_insert_header('Authentication-Results', $authres);
}