Changes have been made in Git for this ticket:

Request #8092: Use CATENATE (RFC 4469) to strip MIME parts
Even if IMAP server doesn't support CATENATE, use the same process to
build the message data as with CATENATE - by defining the parts on the
server using IMAP URLs.

http://git.horde.org/diff.php/imp/docs/CHANGES?rt=horde-git&r1=a1d3bb1a9c45b10fb08c741b075aa02da2c8e561&r2=6d09e5a4cff91180789155a863ef6e65d9ff7864
http://git.horde.org/diff.php/imp/docs/RFCS?rt=horde-git&r1=0268b57d8b60efcb8f57929b68669a5c949347d2&r2=6d09e5a4cff91180789155a863ef6e65d9ff7864
http://git.horde.org/diff.php/imp/lib/Message.php?rt=horde-git&r1=b852ce0f8affdeb57cc473ba287b65d16d382fc0&r2=6d09e5a4cff91180789155a863ef6e65d9ff7864
http://git.horde.org/diff.php/imp/message.php?rt=horde-git&r1=e757952b380548678ba622fe18949030296b3c83&r2=6d09e5a4cff91180789155a863ef6e65d9ff7864

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