How to ignore Content-Transfer-Encoding when the text(mail) crawling

[anatomo]

Hello @marevol.

After I asked #1442, I decoded mail files to utf-8 before crawling. And crawl these files.
But, Maybe the crawler looks parse mail header (the header part has other encoding type).
So, Could you advise how to ignore Content-Transfer-Encoding or Mail Header?
(I want to crawling these files as text/plain or utf-8.)

When crawl this file, It looks good.
test1.txt

But crawl this file, It does not show message part (digest field does not have message part).
test2.txt

thanks.