[exim] Emails starting with a byte order mark (BOM)

Hello,

spammers found another way to annoy sysadmins: I get a rather large number
of mails starting with a Unicode byte order mark (BOM) as first character
of the data. While exim has no problems with them the cyrus lmtp daemon
rejects them (which is IMHO the right thing to do).

The mails look like

Received: from video.XX.com ([64.34.XX.XX] helo=gen3.XX.com)
        by relay.ZZZ with esmtp (Exim 4.80)
        (envelope-from <huxd@YYY>)
        id 1WIJRL-0005Dw-MW
        for XX@YY; Tue, 25 Feb 2014 15:57:00 +0100
<EF><BB><BF>Received: from [10.0.0.100] by gen3.XXX.com id K1sdIgJUfdo1; 
Tue, 25 Feb 2014 08:56:59 -0600
Message-ID: <...@gen3.XXX.com>

The top "Received"-line is added by my server, so the first lines after the
DATA command would be

U+FEFF Received:

exim even recoded this to 0xEF 0xBB 0xBF, but I would prefer to reject
these mails with an ACL. Is there a way to achieve that in an ACL? verify =
header_syntax seems not to work.

Regards
    Michael