Outgoing mail servers are known as SMTP ( Simple

Mail Transfer Protocol ). Incoming mail server come

into main server is known as POP3 ( Post Office

Protocol version 3).

Most POP3 server can store massage on server.

network to allow client to make indirect network

connection to other servers.

Client request to proxy server and proxy server

provides different data like as file, connection etc.

Proxy server passes request and responses

unmodified is usually called gateway.