Network tarpitting can be challenging to implement within an email server, since each SMTP connection is processed more slowly than normal, often holding up precious system resources such as memory and CPU. Because SMTP proxies can be implemented using lighter-weight programming techniques such as asynchronous IO (for example nginx, Node.js, Netty and Libevent), thousands of connections can be juggled using the same resources as a much smaller number of connections in the context of a full-blown store and forward email server.