[Exim] 4.31 and connection lost errors

I have been seeing a large number of connection lost errors in
my logs lately and wonder if anyone can shed some light on what
may be causing these errors. They are happening at a fairly good
rate:

Jul 13 13:07:34 mail exim[16914]: 2004-07-13 13:07:34 H=(aonix.de)
[211.173.173.71] incomplete transaction (connection lost) from
<hinesvh@???>
Jul 13 13:07:34 mail exim[16914]: 2004-07-13 13:07:34 unexpected
disconnection while reading SMTP command from (aonix.de)
[211.173.173.71]

I have tried to use all the logging options with no help on tracking
the cause of these down. I am a little worried that valid email may be
lost when this happens. I hadn't made any configuration changes prior
to this happening.

This is a FreeBSD 4.9 server.

Regards,
Jeff