How to debug 'ignoring non-mail file' issues

[Perttu Luukko]

Hi,

I indexed my archive of emails from recent years with notmuch (about 10k
messages so not much). I have quite a lot of messages 'notmuch new'
ignores as non-mail files, about 1000 of them. They are not obviously
malformed, meaning that the files certainly look like emails when opened
in a text editor. I'd like to find out why these files are ignored, and
if there is something I can do to fix them. Of course I'd like to have a
complete database of my old emails, with nothing falling through the
cracks like this.

The vast majority of these ignored mails are not ignored after I
transfer them with offlineimap to another computer. I can non-ignore
these files probably by copying the renamed file back to the mail
server, so this is fixable. Offlineimap shouldn't mess with the file's
contents, so is there something that can cause notmuch to ignore a file
based on its name?

Looking at the rest of the ignored messages most of them seem to have
very large attachments, but there are possibly others. There is only
maybe 20 of these kinds of emails so I can try to fix them manually.
Still, it would help if I knew what exactly caused notmuch to ignore the
file. I understand most of the message parsing is done with gmime. Does
gmime give any diagnostics on parse errors that could be used to give a
reason for thinking a file is not mail?

I understand that the list of non-mail files is stored in the notmuch
database and the files are completely ignored from there on. This
actually makes it harder to debug these kind of issues since the list of
ignored mails is only visible on the first invocation of 'notmuch new',
unless the files are moved around. Is there some way to extract the list
of ignored files from the database for inspection? Maybe 'notmuch new'
could have some kind of --unignore-non-mail switch that would reconsider
previously ignored files.

-- 
Perttu Luukko