On the trail of a searching problem, I enabled debugging with make CFLAGS="-g -DDEBUG" CXXFLAGS="-g -DDEBUG" Now it seems that any search that is non-empty (i.e. matches something) crashes with a duplicate In-Reply-To ID. This is in git revision 92c4dcc (although it was the same yesterday). The oddest thing is that the second message-id is a common English word. Here is a trace dulcinea:~/tmp % ~/projects/notmuch/notmuch search spam Query string is: spam Final query is: Xapian::Query((Tmail AND Zspam:(pos=1))) Query string is: thread:13c033781712e92541a5591320ac0ff4 Query string is: thread:13c033781712e92541a5591320ac0ff4 AND (spam) Final query is: Xapian::Query((Tmail AND 0 * G13c033781712e92541a5591320ac0ff4)) Final query is: Xapian::Query((Tmail AND 0 * G13c033781712e92541a5591320ac0ff4 AND Zspam:(pos=1))) Internal error: Message 877htzhn9e.wl%jemarch@gnu.org has duplicate In-Reply-To IDs: 1e5bcefd0911081424p12eb6fa9te57ff4cfeb83fcdd@mail.gmail.com and data (lib/message.cc:326). At the moment I don't have any real good ideas for how to debug this (or any real familiarity with notmuch internals). I put a test corpus of messages (all from public mailing lists) at http://pivot.cs.unb.ca/scratch/mailtest.tgz The current tarball is about 5M. The machine has plenty of bandwidth (not meant as a challenge to DDOS hobbyists :) ). d