Open Relay Agent

A method of accessing electronic mail or bulletin board messages that are kept on a (possibly shared) mail server. IMAP permits a “client” email program to access remote message stores as if they were local. For example, email stored on an IMAP server can be manipulated from a desktop computer at home, a workstation at the office, and a notebook computer while traveling, without the need to transfer messages of files back and forth between these computers. IMAP can be regarded as the nextgeneration POP. A protocol used to transfer email messages from an email server to an email client.
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The Internet email protocol. The primary protocol used to move email messages from clients to servers and from server to server.
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A set of communications protocols that encompasses media access, packet transport, session communications, file transfer, electronic mail, terminal emulation, remote file access, and network management. TCP/IP provides the basis for the Internet. The structure of TCP/IP is as follows: Process layer clients: FTP, Telnet, SMTP, NFS, DNS; Transport layer service providers: TCP (FTP, Telnet, SMTP), UDP (NFS, DNS); Network layer: IP (TCP, UDP); and Access layer: Ethernet (IP), Token ring (IP).
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Proxy server is a server that acts as an intermediary between a remote user and the servers that run the desired applications. Typical proxies accept a connection from a user, make a decision as to whether or not client IP address is permitted to use the proxy, perhaps perform additional authentication, and complete a connection to a remote destination on behalf of the user.
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An email server that relays messages where neither the sender nor the receiver is a local user. A risk exists that an unauthorized user could hijack these open relays and use them to spoof their own identity.
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