What should proxy server administrators consider when configuring proxy servers for various services?

What will be an ideal response?

A network must have one or more proxy servers available for each service protocol proxied on the network. The exact mixture of servers will depend on the needs of the configuration. For instance, a dedicated proxy can handle one type of traffic that is especially vulnerable to attack, such as SMTP. Services that receive an especially heavy load, such as HTTP, might also run more efficiently if given a dedicated proxy server (such as Squid) designed to work especially with HTTP. More commonly, though, organizations use a general-purpose firewall that includes a proxy server that monitors all inbound and outbound traffic. You should certainly configure HTTP and DNS, as well as SMTP and POP3, for e-mail.