Biztalk 2004 S/MIME Signature

A partner is sending us a SMIME signed Biztalk message,
but the content-type is wrong, here is the message:

Connection: Keep-Alive
Content-Length: 18670
Content-Type: text/xml
Expect: 100-continue
Host: www.netixone.com.pt:8888
User-Agent: Microsoft BizTalk Server 2004 3.0.1.0

MIME-Version: 1.0
Content-type: application/pkcs7-mime; smime-type=signed-data;
name="smime.p7m"
Content-Transfer-Encoding: base64

MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGS....

The first content-type is text/xml????
Any help will be apreciated.
Regards,
Benoit.

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