alLANBilling (based on fprobe-ulog flow-tools MySQL) is a tool that can help you to count direct traffic (like e-mail) for your small business.
How it works:
1. Capturing information (NetFlow) from the iptables via ULOG (recommended) by the fprobe-ulog
2. Sending this information (NetFlow) to the "recorder" flow-capture (flow-tools)
3. Exporting information from the recorded flow-files to the MySQL database by the flow-export (flow-tools)
4. Using PHP and Apache to display information from the database (MySQL)