How about using a Content-Description: field instead to carry the file name
information?
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From: John Gardiner Myers
To: ietf-smime(_at_)imc(_dot_)org
Subject: The "name" parameter
Date: Friday, July 25, 1997 3:05PM
Section 3.2.1 mentions the ``optional "name" parameter to the
Content-Type field''. Per the MIME spec, the "name" parameter is not
applicable across all content types, it only applied to particular media
types. The parameter is obsolete, besides.
The SHOULD directive refering to the "name" parameter should be simply
removed from the document.
In "A proper S/MIME implementation MUST use the MIME types and should
not rely on the file extensions." the word "should" should be written as
"must".