I have Exchange server 2010. In Protocol Logs\SMTPReceive on Edge server I see message '504 5.7.4 Unrecognized authentication type' from one IP address. let say that in few minutes I have 400-500 this messages from that IP only different port is used.
My question is: how can I block this IP from even attempting to authenticate?
I know for IP Block List, but when I enetr this IP address in the block list, it doesnt block IP from authenticate.