use Unix::Syslog qw(:macros :subs);
sub is_valid_host
{
    my $host = shift;
    return undef unless $host;
    my ($name,$aliases,$addrtype,$net) = gethostbyname($host);
    defined $name;
}

sub my_envrcpt_callback
{
    my $ctx = shift;

    my $rcpt_addr = $ctx->getsymval('{rcpt_addr}');
    my ($fqdn) = ($rcpt_addr =~ /\@(\S+)/);

    if (not is_valid_host($fqdn))
    {
        # no such machine?
        syslog LOG_INFO, "$$: Rejected mail for $fqdn";

        return Sendmail::PMilter::SMFIS_ACCEPT;
    }

    Sendmail::PMilter::SMFIS_ACCEPT;
}