>> When I run notmuch I get a bunch (hundreds) of emails that are 
>> ignored
>> with:
>>
>> Note: Ignoring non-mail file: ...
>>
>> The files are valid maildir files but have a paragraph somewhere in 
>> the
>> body where someone has written "From ".
>>
>
> And do they also have have a line starting with "From " as the first
> line? This makes them mbox files. The second "From " makes them mbox
> files with multiple messages. Notmuch thinks your MDA (the thing that
> made those files) is misconfigured, assuming my guess about the format
> is correct.

Every message file begins with “From “. This is true of all messages 
downloaded by both offlineimap (with type = Maildir) and mbsync.
neomutt has no issues dealing with these files as maildir and mu has no 
issues indexing them either. I’m assuming that stating with “From 
“ is part of the maildir spec.

The problem occurs specifically with notmuch. If someone sends a message 
with a line that begins with “From “ in the *body* then it confuses 
notmuch.

mu can correctly index these messages but my mu is linked against 
libgmime-2.6, my notmuch (0.28.3) is linked against libgmime-3.0.


>> Is there a fix to force the recognition of maildir files in this 
>> case? I
>> thought this was a solved problem with gmime since 2.6.7.
>
> There is not currently a way to do that. It's not a GMime problem, 
> it's
> a design choice of notmuch to avoid parsing multiple message
> mbox's. That was originally added as a safety feature, and I think it
> should probably stay the default. If someone wants work on adding a
> configuration switch I can point them in the right direction.

This is a poor design decision. It means anyone on the internet can 
break your mail setup simply by sending a message with a line starting 
with “From “.
(and using usual quoted-printable Content-Transfer-Encoding).

Try it. Send yourself a message with the line “From bad parsing comes 
chaos” and see if your notmuch can find it. My version can’t.