Email was originated in the early 1970’s through the Mail Box Protocol which was used for sending documents for remote printing. Later on, more sophisticated methods were developed. Now, the following Internet protocols are used for sending and receiving email: Simple Mail Transfer Protocol (SMTP), Post Office Protocol (POP), Internet Message Access Protocol (IMAP), and Multipurpose Internet Mail Extension (MIME).
Simple Mail Transfer Protocol (SMTP) is the protocol used to transfer email messages from a client to the SMTP server which is then the one responsible for sending the message to the intended server receiver. Regardless of how many mail gateways are in the path, an independent SMTP connection can be used between each host for the message to be moved closer to the intended recipient. Each session with SMTP shall involve a dialog between two mail daemons, one acting as the client and the other as the receiver. Multiple messages may be transferred between these two hosts within one session.
Post Office Protocol is the client mail application which is used to receive or retrieve the messages from the previous SMTP server. This is also referred to as POP3 as it is the third version of the protocol. While clients use SMTP to send the outgoing message to an SMTP server, POP3 is used to retrieve this message. This protocol operates from one state to another depending on the results of the transaction in progress and commands issued in all of its sessions. The first state is authorization wherein the user inputs the username and password to authenticate the client to the mail server. From the original implementation, POP3 supports clear-text for username and password transmissions. Later on, security issues arise and other techniques are suggested to secure the username and password. In the transaction state, the client sends commands and receives responses from the server. Lastly, in the update status, the client has finished its commands and the server is authorized to delete messages that were marked by the client for deletion and closes the TCP connection.
Internet Message Access Protocol (IMAP) is used to store messages on a server. With the use of IMAP, a client can view the header the email message, download to read the entire message and store to the server, or just read it later. This protocol also allows the client to create folders where the server can store the messages.
Multipurpose Internet Mail Extension (MIME) was developed with the aim to address one deficiency of SMTP— inability to attach non-text messages other than ASCII format of files. However, MIME is an extension of the SMTP-based mail system and not a complete substitute to the previously used protocol. It extends the email technology by supporting different types and other complex message bodies. Some of the specifications of the protocol include new message header fields, new content formats, and new transfer codes. New header fields give the information about the actual message body. The new content formats include text, audio, video, Jpeg and .doc formats. Lastly, new transfer codes enable data to be re-encoded or compressed to much smaller size format.
When an email message arrives at its destination, the mail server’s software gives the details of distributing the message locally. When the server receives a new message, it will not be immediately saved into the client’s Internet device. Rather, the message is kept on the mail server. When the client logs in with the use of Internet device, it serves as a request to the mail server to deliver any new messages. This Internet device may be mail client software or email program. The delivery of messages is made possible by email address protected by username and password known only to the client.
Sending messages involve addressing and composing the message. In some cases, it may not be immediately sent depending on how the program or devised is configured. It may be queued to be sent after exiting the program of logging in again. With the option of the client, the message may be saved the drafts folder. On the other hand, receiving involves another process. When a client receives a mail, it is held on the mail server until the email program of the client requests for the new messages. After receipt of the message, it will either be deleted or marked as reading or delivered. Sent messages will be facilitated by SMTP while received messages will be processed by POP3. Sent messages have more detailed email components such as header, TO, CC and others.
Phishing emails are becoming more and more common. Get to know more about emails and phishing through this video below: