TCP/IP - Transmission Control Protocol / Internet Protocol
creates a connection between sender and receiver using port numbers for a particular device; ie: SMTP Port 25
 

IP - Internet Protocol prepares a packet (datagram) for transmission across the Internet with the IP header encapsulated. The IP packet is then passed to the next layer where further network information is encapsulated onto it.

Protocol a method of sending and receiving data.
 

Open relay - mail server that allows anyone to use it to relay emails anywhere (normally, hijacked by spammers) for relaying mails to hundred of thousands or millions of recipients.
 

POP3 - Post Office Protocol Version 3 rfc1939 used for delivering messages to (client) mail readers (fetch mails from a remote mail server and store it locally). The email client sends a login (UserID) and a password to authenticate the session. If accepted--the mail client send commands to retrieve messages, then the server transfers the messages and deletes them from the mailbox.

APOP is a POP3 setting that encrypts your username and password, an authentication mechanism designed to protect your POP3 account password when checking mail.
 

MX or Mail Exchangers are database records (registered domains in the "server identity" bank) particulars of domain names of mail server running with SMTP responsible for a domain or a block of domains.
 

Mail readers - or mail user agents allows you to read emails residing in your remote mail server mailbox, or to retrieve it into your computer with a mail client.
 

Mailbox - each mailbox is assigned a unique address ie: mymail@mydomain.com character string which identifies the user to whom the mail is to be sent. Mailboxes normally reside on mail servers that are always connected to the Internet and mails are retrieved by the user mail client from the remote mail servers using (POP3) Post Office Protocol
 

Mail readers or mail user agents allows you to read emails in your mailbox on the mail server or on your pcs.
 

User Agent - A program (ie: Eudora) or editor that let users create, edit, compose, store and send mails to a mail server, polls a mail server for mails, download and display mails, as well as using POP3 to talk to mail servers. Basically, the function of emails consists of 2 parts--User Agent and--MTA --that prepares and send emails.
 

MTA - Message Transfer Agent the exchange of mail using TCP/IP is performed by MTA that defines how email messages are transmitted between two users.
 

MAC (Media Access Control) manages one of the sublayers handles access to shared media.
MAC address are 6 bytes long and are controlled by the IEEE. It is a standardized data link layer address that is required for every port or device that connects to a LAN. Other devices in the network use these addresses to locate specific ports in the network and to create and update routing tables and data structures. MAC address are also known as; Hardware address, MAC-layer address or Physical address.
 

ARP - Address Resolution Protocol translates an IP packet address into a MAC layer address so that frames can be delivered to a LAN destination workstation.
 

NAT - Network Address Translation allows a router that represent an entire LAN to the Internet--to act as a single IP address. When a packet is sent-out from a LAN the NAT interface changes the internal address to a global IP address. Since a LAN cannot be seen from the outside, the internal IP addresses need not be registered. The normal range of private addresses:
10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255  See Private Network
 

Firewall - A hardware or software device which regulates data flowing into and out-of a private network.

Telnet - A program that allows a user to remotely login into a distant and remote computer site (usually a password and login ID is required).

Throughput - The outgoing & incoming datagram (bits & bytes) between; your computer, ISPs connection and the Internet network.

MaxMtu (MTU) Maximum Transmission Unit - is the default packet Windows uses to negotiate when a connection is opened between two computers, they must agree on an MTU by comparing MTU and selecting the smaller of the two. If it is set too large for routers, it is then fragmented into packet size and can take double the amount of time it takes to send a single packet.

UART Universal Asynchronous Receiver Transmitter Data flow between the serial port and the modem is governed by a UART chip, which can contain no data buffers, single-byte data buffers or 16-byte data buffers. All data flows between the serial port and the modem via the UART

RWIN (TCP Receive Window) determines how much data the receiving computer is prepared to receive. RWIN value that is set too high will result in greater data loss if the packet is lost or damaged in transit. RWIN value that is set too low will produce poor throughput.
 

MSS (Maximum Segment Size) is the largest segment of TCP data that Winsock is prepared to receive on a particular connection. When the TCP connection is initially established, both uses the minimum of each other's MSS value. If the MSS is too low, the data/header ratio will be low. If the MSS is too high, will lead to large IP datagram and the packets will tend to fragment in transit where other networks may be having smaller MaxMtu - Hence, performance can be increase by reducing MSS value.
 

TTL-Time To Live, is a field in the IP header which indicates how long a packet should be allowed to survive before it is discarded. TTL essentially determines the maximum number of hops permitted.
 

ICMP - Internet Control Message Protocol are used by routers and nodes to perform error reporting for Internet Protocol. It report errors such as invalid IP address, invalid port address, and the packet has hops too many times.
 

RFC - Request For Comments, a series of officially defined technical documentation on Internet standards.
 

SMTP - Simple Mail Transport Protocol a protocol governing email transmission and reception (sending and receiving emails between mail servers).

SMTP return error codes lists

Winsock Error Codes - return error codes by Windows Sockets API WSAGetLastErrorcall lists.

ESMTP, SMTP Connect and Data Receive, Reply Codes Command Groups lists

Port Numbers are services that a machine performs by a program by listening on a port. A port number is actually a number between 1 and 65535 which identifies to the receiving computer what function you want it to perform.

Router or gateway is a hardware device that forwards packets from one network to another. IP uses a routing table to determine which networks that packets can be forwarded to and will only forward them to networks that it has been configured to do so.

Server-time-out - The sending and receiving mail server are busy and having different timeouts, when one of them gives up while the other is still trying--resulting in the connection being terminated unexpectedly. Or the "receiving or sending" mail server terminate the connection due to imposed limits by time or quantity of mails.
 

Mail Host - An Internet SMTP mail server computer on which mailboxes reside and each host has a mail server which can receive mails and store them--for delivery (relay) to corresponding mailboxes or internal mailboxes.
 

Mail server receive, stores and transmits email, it is a computer that is independent of your PCs and sitting somewhere in a building--managed by your Internet Service Provider or corporate IT department. You can use any PCs to get at the Mail Server for sending or receiving email from any location.
 

Email exploders - Software programs that maintain mailing lists in a database that receive emails and forward them to each member in the list.

Email gateway - A computer dedicated to processing emails to manage and maintain large mailing lists database without human intervention, ie: auto receive and forwards mails, users subscriptions or unsubscribe, etc.

Listserv - A software program used for creating and managing Internet mailing lists, ie: An individual sends an email to a listserv; it then sends a copy of the message to all listserv members.

Server - A computer that serves other computers. A Host server stores web sites.

sendmail - A software program for sending emails.

Command - is a request for mail service action sent by the sender SMTP to the receiver SMTP

UDP - User Datagram Protocol, transport protocol used in place of TCP for wireless connection applications, it also encapsulates a "simple" header onto an application packet.

FTP - File Transfer Protocol, are commands for software programs that let users transfer files across the Internet (upload or download files). The most common ways to access a FTP is through a "browser", an FTP program or by issuing FTP commands at a text-based command prompt.

ISP - Internet Service Provider a company that provides any kind of access to the Internet, such as dial-up modem, cable modem, hosting, etc.

Web server - A host that store web pages or sites and wait for a browser to opens a connection that request a specific page, it then send a copy of the requested item and closes the connection.

URL - Uniform Resource Locator consist of some "Text" followed by the "colon" -- it is a communication protocol that tells a (ie: web-browser, email clients) program residing in a computer what to do.

HTTP - Hyper Text Transport Protocol. URL is entered into a browser--it asks DNS for the IP address using the IP name in the URL, makes a TCP connection to port 80 of a remote host specified by the IP address, connect to the web server, send a GET command and the web server sends the webpage, the browser close the TCP connection and displays the webpage.