Digitally signed emails send as attachments

When sending a digitally signed email , the recipient receives an email with an attachment (.msg or .zip file) instead of text appearing in the body of the email.  No encryption is being used and when sending to others in our organization, this problem doesn't occur.  Our mail servers are using Exchange 2007 which was recently migrated from Exchange 2003.  We did not have this issue prior to Exchange 2007.  Outlook 2007 is the email client being used to send email.  Is there a setting in Outlook or on the Exchange servers that is causing the issue?
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Do you apply disclaimers in a transport rule?

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sdrummond56Author Commented:
No, we do not use a disclaimer
Any transport rule?
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