[Exim] how to remove the ">From : " line for the smtp driver

I'm using 3RSoft's Mail Studio web mail package with EXIM 3.33, but I found
the combination will produce mail header with a blank line and then a

>From chunsang@??? Tue Dec 04 15:18:45 2001

line.

when read by mail clients, the subject line is gone and the message body
will displayed something like:

Subject: =?iso-8859-1?B?dGVzdCB0ZXN0?=
Date: Thu, 29 Nov 2001 13:25:48 +0800
MIME-Version: 1.0
X-Priority: 3
X-Mailer: @MESSAGE-5.0.0905.1.2400 (Linux 2.2.12-20)
Content-Type: multipart/mixed;
        boundary="----=_NextPart_QALXL2WTRH8PRWODO1XC9ROV"

This is a multi-part message in MIME format.

------=_NextPart_QALXL2WTRH8PRWODO1XC9ROV
Content-Type: multipart/alternative;
        boundary="----=_NextPart_KPX56FN3FE687S74Z4IWPDZJ"

------=_NextPart_KPX56FN3FE687S74Z4IWPDZJ
Content-Type: text/plain;
        charset="iso-8859-1"
Content-Transfer-Encoding: base64

dGVzdCAKCgpEbyB5b3Uga25vdyBATUVTU1NBR0U/IFBvd2VyZWQgYnkgM1IgU29mdCwgSW5jLgoK

From previous postings, I learned that for the appendfile driver, I can use
check_string and escape_string to remove the ">" sign and solve the problem
for the case of mailing to local users, but for remote users, which will use
the smtp driver, how do I remove the ">" sign?

Thanks

Ernest Wong