The Access Controls section allows for very fine-grained tuning of access to the server. Access to the server can be denied or granted based on the recipient address, sender address and the IP address or hostname of the SMTP Client.
The main menu has two main options on it. Enable Recipient Address Controls and Enable Sender Address Access Controls. Below the buttons are the sections for configuring both these options, which are inaccessible until they are enabled. SMTP Client Access is always enabled.
You need to enable Recipient Address Access Control and Sender Address Access Control before using them.