For the past few days, we are getting huge number of connections to port 25. There are almost 500 to 700 connection to port 25. These are coming from different IPs. I have tried blocking several IPs, but the attack are coming from different IPs, so that didnt make much difference. When a client tries to connect to port 25 he is getting "421 Too many concurrent SMTP connections; please try again later." What can I do to limit this. Please advice.
