[exim] why so many synchronisation failures?

I am seeing a large number of synchronisation errors in incoming mail
eg
rejected connection from H=[198.53.60.171] input="QUIT\r\n"

The IP address varies but the QUIT\r\n is the commonest version, and
overwhelmingly from places with no reverse DNS.
I am sure this is unwanted stuff, but what are the malefactors trying
to achieve?


=John ffitch