I've installed a Debian GNU/Linux server with postfix+courier-ldap+amavis+clamav. The server receive 8000 good mail and 150000 spam mail per day. I have a problem with smtp session. There are normaly 30 smtp active session and sometimes the client can't send email. 'SMTP error...'
We'll need the error if you expect us to help. You might try adjusting the number of smtpd's limit in the master.cf file. The default might be too low for your installation.