If CATENATE IMAP extension is available, use it to strip MIME parts.   
From Appendix A of RFC 4469:



    Example 3: The following example demonstrates how the CATENATE

    extension can be used to strip attachments.  Below, a PowerPoint

    attachment was replaced by a small text part explaining that the

    attachment was stripped.



    C: A003 APPEND Drafts (\Seen \Draft $MDNSent) CATENATE

     (URL "/Drafts;UIDVALIDITY=385759045/;UID=21/;section=HEADER"

     TEXT {42}

    S: + Ready for literal data

    C:

    C: --------------030308070208000400050903

    C:  URL "/Drafts;UIDVALIDITY=385759045/;UID=21/;section=1.MIME"

     URL "/Drafts;UIDVALIDITY=385759045/;UID=21/;section=1" TEXT {255}

    S: + Ready for literal data

    C:

    C: --------------030308070208000400050903

    C: Content-type: text/plain; charset="us-ascii"

    C: Content-transfer-encoding: 7bit

    C:

    C: This body part contained a Power Point presentation that was

    C: deleted upon your request.

    C: --------------030308070208000400050903--

    C: )

    S: A003 OK append Completed