A machine may have one or more IP addresses associated with a network card. For example:
127.0.0.1 - Every machine has this address and is called the loop-back address
When you run a server on a machine it listens for incoming client connections. Administrators can selectively pick which IP addresses a server process listens on. This selective picking is called binding. For example, if you just bind to the loop-back, clients running on the same machine can connect to the server
Binding to a specific IP address in Xeams
The SMTP as well as the SMTP Proxy server in Xeams can be bound to a specific IP address on the machine. To bind to an IP, specify the value for Bind To field.