[exim] rejected messages get delivered nonetheless

Hello,

I'm seeing log messages like this frequently:

2007-04-17 13:34:10 SMTP protocol synchronization error (next input sent
too soon: pipelining was advertised): rejected "" H=(******) [******]
next input="*************"

(I replaced the host addresses and the message content in this log entry
with stars *).

I'm fine with exim rejecting the message; however the message gets
delivered nonetheless to my local mailbox. The problem is then that the
remote host will continue retrying to deliver the message, each time
failing it because of the same synchronization issue, and each time
causing a (presumably incomplete) message to be delivered to the local
mailboxes.

The version used is 4.63. The configuration is quite similar to the
example described in the manual.

Am I doing something obvious wrong? How can I tell exim not to deliver
messages that have been rejected in the first place?

Thanks for any help

td