What does the error too many unrecognized commands mean?

There have been instances of network abuse involving mail sent out by web servers. In most cases, unrecognizable commands are sent as part of the SMTP session. A real MTA never sends out such invalid commands. Exim allows a few unrecognized commands in a session to permit humans who are testing to make a few typos (it responds with a 5xx error). However, if Exim receives too many such commands, it assumes that it is dealing with an abuse of some kind, and so it drops the connection.