[exim] Too many syntax or protocol error.

Hi,

Does anybody seen this err in the rejectlog before:

2004-10-26 15:10:22 SMTP call from [207.136.202.146] dropped: too many
syntax or protocol errors (last command was "??")
2004-10-26 15:14:45 SMTP call from [203.255.10.96] dropped: too many
syntax or protocol errors (last command was "??")
2004-10-26 15:15:29 SMTP call from [220.178.76.18] dropped: too many
syntax or protocol errors (last command was "??")

What does it mean?

Sam.