- \n
- ARPANET was the stage on which the early messaging protocols were developed.<\/li>\n
- SMTP was the first major advance to simple File Transfer Protocol and was designed specifically for internet messaging.<\/li>\n
- POP3 and IMAP are later protocols developed to provide more robust security, access, and interaction<\/li>\n
- Popular consumer applications like Gmail, Outlook, and Thunderbird all facilitate the usage of these protocols in abstracted user interfaces.<\/li>\n<\/ul>\n
Quick History<\/h2>\n
![\"internet](\"https:\/\/www.alpharithms.com\/wp-content\/uploads\/262\/internet-message-processor-original-ucla.jpg\" "\\"internet-message-processor-original-ucla\\"")
The front panel of the first IMP machine used at UCLA<\/figcaption><\/figure>\n In 1958 the U.S. Defense Department (DoD) founded the Advanced Research Projects Agency (ARPA) (DOD Directive 5105.15<\/a>). ARPA was billed as an agency to “to help maintain U.S. technological superiority and guard against unforeseen technological advances by potential adversaries.” At the time this likely wholly referred to Russia’s Sputnik program.<\/p>\n
ARPANET is Created<\/h3>\n
In 1969, ARPA contracted BBN Technologies to build the first routers which allowed scientists to connect “geographically separated” computers. This was called ARPANET<\/a> and shortly thereafter transformed into the earliest expressions of the Internet we know today.<\/p>\n
First Network Created<\/h3>\n
The initial ARPANET network was a four-node design consisting of Internet Message Processors (IMP)<\/strong> located at UCLA, Standford, University of California at Santa Barbara, and the University of Utah. The first successful network message transmission<\/strong> between separate machines occurred on October 29, 1969.<\/p>\n
TCP\/IP is Born<\/h3>\n
In 1973 DARPA, having been re-branded a year prior, introduced the TCP\/IP protocol<\/a>. This project was done in collaboration with researchers from Stanford University. The TCP\/IP protocol remains the foundation of much of the modern Internet’s communications<\/a>\u2014including a large portion of modern Internet Mail Exchanges.<\/p>\n
Localized Message Services<\/h2>\n
Before there was email, there were internetwork communications. Initially, users would log on to a shared resource and save files in a local directory with names like ToAlice<\/em>\u00a0or ToBob\u00a0<\/em>indicating the desired recipient. The follow-up to this rudimentary system came in 1965 when MIT researchers developed the MAIL command as outlined in a circulated staff note circa 1965:<\/a><\/p>\n
A new command should be written to allow a user to send a private message to another user which may be delivered at the receiver’s convenience This will be useful for the system to notify a user that some or all of his files have been backed-up. It will also be useful for users to send authors any criticism.<\/p><\/blockquote>\n
This protocol established the basics of the inbox: a user can receive directed messages such that newer ones are differentiated from older ones. While still running around on local networks, this system laid the conceptual groundwork for message queuing that would later serve as backbone services to email and internet messaging protocols.<\/p>\n
Internet Email is Born<\/h2>\n
In a 1971 Request for Comments (RFC196<\/a> ), Richard W. Watson outlined a proposed Mail Box Protocol specifically for the send\/receipt of textual messages. This RFC outlined such aspects of the Mail Box Protocol as follows:<\/p>\n
- \n
- Sequential user files to which new messages would be appended<\/li>\n
- Transmission format of 7-Bit ASCII in 8-bit bytes<\/li>\n
- Endlines, newlines, and site-specific encoding opportunities<\/li>\n
- Message width and document length<\/li>\n
- Transmissions protocols<\/li>\n
- Connection lifespan<\/li>\n
- Mail Box numbering systems<\/li>\n<\/ul>\n
The backbone of early email messaging was done via File Transfer Protocol outlined in the 1972 RFC354<\/a>. This outlined the new usage of several existing protocols to form a more useful data transfer protocol. The existing protocols were HOST-HOST, Initial Connection Protocol, and TELNET. This RFC outlined FTP as the following considerations:<\/p>\n
- \n
- Establishing Data Connections<\/li>\n
- Data Representation & Storage<\/li>\n
- File Structure & Transfer Modes<\/li>\n
- Error Recovery & Restart<\/li>\n
- Files Transfer Functions<\/li>\n
- FTP Commands<\/li>\n
- Access Control Commands<\/li>\n
- Data Transfer Commands<\/li>\n
- FTP Service Commands<\/li>\n<\/ul>\n
This document laid the groundwork for describing a protocol that would then be used as the backbone of early internet messaging services.<\/p>\n
In a later RFC469<\/a>, further specifications were made that include the use of several new additions to the File Transfer Protocol that was sending\/receiving messages:<\/p>\n
- \n
- @<\/strong> – to denote user\/host relationships<\/li>\n
- TO<\/strong> – to address the recipient<\/li>\n
- FROM<\/strong> – to denote the sender<\/li>\n
- AUTHOR<\/strong> – to denote possible multiple message authors<\/li>\n
- TITLE<\/strong> – the early term for “subject”<\/li>\n
- ACKNOWLEDGEMENT<\/strong> – protocol for notifying the sender of a transmission success<\/li>\n
- RECORDED<\/strong> – optional field to store a copy on network servers<\/li>\n
- TYPE<\/strong> – sender direction for how the message should be stored (long, urgent, short)<\/li>\n
- TEXT<\/strong> – the field for the main body of the message<\/li>\n<\/ul>\n
Simple Mail Transfer Protocol<\/h2>\n
Unsecured Port<\/strong>: 25<\/p>\n
Secured Port<\/strong>: 465<\/p>\n
In 1981, Jonathan B. Postel officially laid out the Simple Mail Protocol in RFC 821<\/a>, the contents of which are not brief. This proposal stood to revolutionize the current FTP system in a way that would be much more specific to mail-sending based needs. Among many outlined procedures, RFC821 outline the following:<\/p>\n
- \n
- Forwarding<\/li>\n
- Verification<\/li>\n
- Opening & Closing messages<\/li>\n
- Message Relaying<\/li>\n
- Domains<\/li>\n
- SMTP commands<\/li>\n<\/ul>\n
The goal of SMTP was to create a system to transfer textual messages reliably and efficiently. SMTP was seen as an evolution of protocol because it was to exist agnostic of the lower network layers and their respective transmission protocols. In other words, SMTP was an application layer service.<\/p>\n
SMTP still uses the 7-bit ASCII<\/strong> model outlined in RFC196 which requires binary data from sender\/receiver sides to be encoded upon transmission and then decoded upon receipt accordingly.<\/p>\n
The SMTP Messaging Model<\/h3>\n
SMTP brought a lot of new concepts to the table. At the core, SMTP was designed to facilitate the communication between two hosts connected via the same transport service. A basic outline of this process is below:<\/p>\n
- \n
- Establish Transmission channel<\/li>\n
- SMTP Sender sends a MAIL command<\/li>\n
- SMTP Receiver responds with an OK command<\/li>\n
- SMTP Sender sends RCPT command, identifying the intended recipient<\/li>\n
- SMTP Receiver responds with OK if the message can be received<\/li>\n
- SMTP sends mail data, using a specific termination sequence<\/li>\n
- SMTP Receiver responds with OK on successful receipt of message data<\/li>\n<\/ol>\n
SMTP uses a Store-and-Forward<\/strong> protocol which is characterized by its PUSH protocol where the messaging service is initiated by the sending server. A user enters a command that is transmitted (Pushed) via the user’s SMTP server to the receiver’s SMTP server. The recipient server can then store the file onto the recipient users’ local file system as shown in the following illustration:<\/p>\n
![\"smpt](\"https:\/\/www.alpharithms.com\/wp-content\/uploads\/262\/smpt-protocol-illustration.jpg\" "\\"smpt-protocol-illustration\\"")
SMTP protocol established the concept of mail servers<\/figcaption><\/figure>\n Initially, SMTP was designed to be a message\u00a0transfer<\/em> service intended to route completed messages between hosts. There was little accommodation for incorrect message formatting or error checking. As SMTP became more popular and its usage more widespread, it was realized more as a message submission<\/em> service. Published in December of 1998, RFC2476<\/a>\u00a0 notes this and outlines a protocol for more robust Message Submission use.<\/p>\n
Post Office Protocol – Version 3<\/h2>\n
- TO<\/strong> – to address the recipient<\/li>\n
- @<\/strong> – to denote user\/host relationships<\/li>\n
![\"pop3](\"https:\/\/www.alpharithms.com\/wp-content\/uploads\/262\/pop3-email-protocol-diagram.jpg\" "\\"pop3-email-protocol-diagram\\"")
![\"imap](\"https:\/\/www.alpharithms.com\/wp-content\/uploads\/262\/imap-email-messaging-protocol-diagram.jpg\" "\\"imap-email-messaging-protocol-diagram\\"")