Problem with attachment in text format

Hi list,

Maybe this question is already in the wiki.I have searched but still didn’t work it out.
I’m using RT 3.4.2.
If my RT receive a mail with text format attachment such as ‘.doc’ or ‘.txt’ file attachment, it will display attachment content as a part of the mail content.
My company need RT to receive and send email with no change no matter what kind of the incoming mail attachment is.
Any help will be very appreciated.