Fix #1478
I changed my original plans a little because I had so many extra ideas and then sorted that I should rather look at actual NDNs and look what is necessary to parse them:
- Recognize NDNs by ~the sender address, which is in a regex the providers database. The problem with heuristics would be that someone could send fake-NDNs and mark messages as failed.~ the standard ("report/delivery-status") and heuristics ("subject contains 'fail' and sender contains 'daemon'"). If there is a valid Message-ID, then rely on that this is an NDN (of course, generally someone might try to find out a Message-ID and send a fake NDN).
- ~Look for `In-Reply-To`~ (only Gmail did this and Gmail uses rfc822 anyway.)
- ~Look for a mimepart `message/delivery-status`, which might contain a `X-Original-Message-ID`~ (only Gmail did this and Gmail uses rfc822, too, anyway.).
- Search through the body and look for a line `Message-ID: *` (remember to remove `<`, `>`), in the hope that that's the original header
- Look for a mime-part containing the string `rfc822`, which will contain the original header. Parse them with Mailparse and look for `Message-ID`.
CLOSE, which was used previously, only expunges messages and deselects
folder, and it should only be called if some folder is selected. For that,
Imap.close_folder() method is used.
This adds functionality to the cffi build script to also extract
defines so that we can ask the compiler to figure out what the correct
values are. To do this we need to be able to locate the header file
used in the first place, for which we add a small utility in the
header file itself guarded to only be compiled for this specific case.
