[Exim] Exim refusing connections

Apologies if this has been asked before
Has anyone seen the following behaviour - exim refusing connections
because smtp_accept_max has been exceeded BUT no messages being received
from the systems that ARE connected. The existing connections appear to
be fully established (i.e. it doesn't look like a SYN attack) and are
not long-lived (i.e they seem to have a maximum duration of 1 or 2
minutes).

Is there logging that I can turn on that will put an entry in the
logfile on every connection (at tcp level and regardless of whether an
SMTP session is started at all)

Thanks in advance
----------------------------------
David Allen
Manager - CMC Systems
Information Services
Queens University Belfast
Belfast BT7 1NN
Phone: +44 (28) 9027 3886
Email: d.allen@???