Limit for smtp connection

[Paulo Fragoso]

Hi,

How can we limit the number of simultaneously accepted
connections from the same IP address to our smtp server?

We are using qmail+daemontools+spamcontrol+qmailscanner+spamd, but 
sometimes there are floods from same IP to our server (smtp port), 
reaching connetions limit configured on tcpserver startup (tcpserver -c 
#). We can't increase this limit because it can kill other process by 
out swap (DoS).

We have found some SMTP server on the internet which accept no more than 
5 simultaneusly connection from our SMTP server. How to implement this 
using qmail+tcpserver?

Paulo.