Take #3 on adding support for messages that lack Message-ID headers to notmuch-mutt. For context see: - http://notmuchmail.org/pipermail/notmuch/2015/thread.html#20171 - http://notmuchmail.org/pipermail/notmuch/2015/thread.html#20079 I've rewritten the patch taking into account the suggestions by Tomi Ollila, who suggested a much cleaner approach for processing headers and possibly fallback to synthetic Message-IDs (thanks Tomi!). I'll be happy to hear further comments on this patch series. If there are none, please merge it into master. Cheers.