[Exim] Format error in spool file (2)

I have three messages in my queue which are showing "Format error in spool file"
errors in eximon and the mainlog. The common feature is that stands out to me is
that non-printing characters are involved.

(Note that the messages arrived under exim-3 and I noticed them while looking for
problems after I changed to exim-4.)

The log shows the messages arriving with (no new lines except where explicitly
stated):

2003-01-21 04:31:00 18aq3v-00PSQl-00 <= return-94258-1616598@???
H=b<two accented characters>
<<<NEW LINE>>>
05.219.10 (freecelebbabes.com) [66.205.219.10] P=smtp s=6027
id=A99CA8AE60A49679171B80FC35F109F4@??? from
<return-94258-1616598@???> a.user@???

In the spool file I have (line breaks are actual this time):

199P Received: from b<same two accented characters>
05.219.10 (66.205.219.10] helo=freecelebbabes.com)
        by hermes.ex.ac.uk with smtp (exim 3.33 #1)
        id 18aq3v-00PSQl-00
        for a.user@???; Tue, 21 Jan 2003 04:30:59 +0000

The problem has corrupted the appearance of the HELO component of the log entry, but
the address component of the Received: line in the spool file. In both files there
is a line-feed where one would not expect one.

Any ideas how I might work out what was in the messages to cause this?

Phil.
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Phil Chambers (postmaster@???)
University of Exeter