Comment 7 for bug 695418

That is nice. So, you need vm-included-mime-types-list to extract
the text. Quoting from the manual:

"By default, VM uses its MIME displaying mechanism to extract the
included text to be cited in replies. If this does not work
correctly, you can set the variable `vm-included-mime-types-list' to
selectively include the MIME types that should be covered in the
included text. The list should have `text/plain' at a minimum and
could include other types such as `text/enriched' and `message'.
Setting the variable to nil returns you to the default behaviour."

I will re-write the doc string for vm-included-mime-types-list to make
this clear.

Cheers,
Uday