Hi David,
Thanks for your quick response.

The double From lines do not seem to be the problem, because when I
remove one of them, no change.

Also, many problem mails do not have double From lines, like the one I
attach below

So again, any idea is highly welcome!
--Axel

>>>>> On Sun, 01 Jan 2017 19:26:07 +0000, David Edmondson <dme@dme.org> said:

    > On Thu, Dec 29 2016, Axel Jantsch wrote:
    >> Hi,
    >> 
    >> I try to build a notmuch database from my nmh files.
    >> 
    >> I have about 220k emails and about half of them is ignored by
    >> notmach new with the note, e.g.:
    >> 
    >> Note: Ignoring non-mail file: /home/jantsch/Mail/ARTEMIS-MPSOC/1
    >> 
    >> Here is the header of that particular email:
    >> 
    >> =============================================================================
    >> From nobody@nowhere  Sun Aug 02 21:21:17 2009
    >> From nobody@nowhere  Sun Aug 02 21:21:17 2009

    > Maybe the double "From " lines?

    >> From: "Axel Jantsch" <axel@kth.se>
    >> Organization: Royal Institute of Technology
    >> To: Joe.Someone <joe@Somewhere.com>
    >> Subject: Re: Artemis and MPSOC 
    >> In-Reply-To: Message from Joe.Someone <joe@Somewhere.com>
    >> of "Tue, 09 Jan 2007 15:10:34 +0100."
    >> <009c01c733f7$edea4340$7766e882@amdht> 
    >> X-Image-URL: http://www.it.kth.se/~axel/axel.png
    >> X-Mailer: MH-E 7.83; nmh 1.0.4; GNU Emacs 21.2.1
    >> MIME-Version: 1.0
    >> Content-Type: text/plain; charset=us-ascii
    >> Content-Transfer-Encoding: 8bit
    >> Date: Wed, 10 Jan 2007 15:47:09 +0100
    >> Sender: axel@bee.imit.kth.se
    >> 
    >> 
    >> Joe, 
    >> 
    >> ...
    >> 
    >> =============================================================================
    >> 
    >> Any idea why so many emails are not recognized by notmuch?
    >> 
    >> Best,
    >> Axel
    >> 
    >> 
    >> -- 
    >> Axel Jantsch, Prof. of Systems on Chip
    >> TU Wien
    >> Gusshausstrasse 27-29/384, 1040 Vienna, Austria
    >> Phone: +43 1 58801 38415
    >> Email: axel.jantsch@tuwien.ac.at
    >> Web: www.ict.tuwien.ac.at
    >> 
    >> _______________________________________________
    >> notmuch mailing list
    >> notmuch@notmuchmail.org
    >> https://notmuchmail.org/mailman/listinfo/notmuch


-- 
Axel Jantsch, Prof. of Systems on Chip
TU Wien
Gusshausstrasse 27-29/384, 1040 Vienna, Austria
Phone: +43 1 58801 38415
Email: axel.jantsch@tuwien.ac.at
Web: www.ict.tuwien.ac.at