[exim] Exim and incomplete transaction

Hello,
Recently I started experiencing problems with Exim on one of our servers.
The exim_mainlog show a lot of:

incomplete transaction (QUIT)
incomplete transaction (connection lost)
incomplete transaction (RSET)

It happens with both existing and non-existing e-mail accounts on the server and I've already had 1 support case from a customer who's collegue tried to mail him and the mail got bounced. The log had "incomplete transaction (RSET)" for that mail.

We have an identical server to this server and that server doesn't have any problems. And I can't think of any changes that's been done on this server that would affected exim.

Here are some examples from the log:

2005-04-21 09:24:35 H=(mrbean.net.au) [221.140.114.102] incomplete transaction (connection lost) from <icannon@???>
2005-04-21 09:24:35 unexpected disconnection while reading SMTP command from (mrbean.net.au) [221.140.114.102]

2005-04-21 00:17:15 H=smtp.1800petmeds.com [65.202.84.121] F=<> rejected RCPT russterrell44@A_DOMAIN_ON_OUR_SERVER: Unrouteable address
2005-04-21 00:17:15 H=smtp.1800petmeds.com [65.202.84.121] incomplete transaction (RSET) from <>

After checking a bunch of these messages it feels like most of these mails are spam though...but some aren't though.

Any idéas? What could I check?

Best Regards
Goran