threading is a risky business

I'm still doing research on the 'missing_thread' mailbox problem. The problem is pretty simple to describe:

1. The thread index requires a mail that is not a reply to start a thread with.
2. The function hashreplynumlookup() (struct.c:362) does it best to look up possible replies.
3. In the problematic mailbox we have identical subjects "Re: Beschwerde" in all three mails, but only one of them with a In-Reply-To: header.

A few selected headers from the three mails:

Subject: Re: Beschwerde
In-Reply-To: <m0vB8kj-0009PcC_at_relay.Boerde.DE> Message-ID: <Pine.A32.3.91.961010183109.52177A-100000_at_graf350.urz.uni-magdeburg.de>

Subject: Re: Beschwerde
Message-Id: <m0vC2i2-0009PcC_at_relay.Boerde.DE>

Subject: Re: Beschwerde
Message-Id: <m0vB8kj-0009PcC_at_relay.Boerde.DE>

4. All this taken together, mail 0 is considered the reply to message 2 and

   the other two are considered replies to mail 0.

I really can't see any good way out from this. Other than not match that willingly on subjects, but that will make hypermail less effective when clients that don't support in-reply-to and similar are used.

Anyone with ideas or suggestions around this?

-- 
             Daniel Stenberg - http://www.fts.frontec.se/~dast
   ech`echo xiun|tr nu oc|sed 'sx\([sx]\)\([xoi]\)xo un\2\1 is xg'`ol