[exim] stopping return receipt

Hi,

We have an Exchange server with Outlook clients behind three Exim gateways.
Exim removes these return receipt headers:

Disposition-Notification-To :
Read-Receipt-To :
Read-Receipt-To :
Return-Receipt-Requested :
Register-Mail-Reply-Requested-By :
Return-Receipt-To

However, Read: emails are still being sent and it is always in response to a email
sent from a Microsoft server and have the following type headers:

X-MS-TNEF-Correlator: <4F5FA1AFEC6EF74FA47A00DB7CE4531005F40839@ti_mail2place.com>
MIME-Version: 1.0
X-Mailer: Internet Mail Service (5.5.2653.19)
Content-Type: multipart/mixed;
    boundary="----_=_NextPart_000_01C67F83.54B1C133"
Return-Path: <email address>
X-OriginalArrivalTime: 24 May 2006 22:41:42.0257 (UTC) FILETIME=[3A528E10:01C67F83]

------_=_NextPart_000_01C67F83.54B1C133
Content-Type: text/plain

------_=_NextPart_000_01C67F83.54B1C133
Content-Type: application/ms-tnef
Content-Transfer-Encoding: base64

+++++++++++++
As you can see there's nothing about a return receipt there. Can anyone tell me how to stop this?

Thanks,
Craig Jackson