Article about email - what it's made of

What is email?

Electronic mail, commonly shortened to “email,” is a communication method that uses electronic devices to deliver messages across computer networks. "Email" refers to both the delivery system and individual messages that are sent and received.

Email has existed in some form since the 1970s, when programmer Ray Tomlinson created a way to transmit messages between computer systems on the Advanced Research Projects Agency Network (ARPANET). Modern forms of email became available for widespread public use with the development of email client software (e.g. Outlook) and web browsers, the latter of which enables users to send and receive messages over the Internet using web-based email clients (e.g. Gmail).

Today, email is one of the most popular methods of digital communication. Its prevalence and security vulnerabilities also make it an appealing vehicle for cyber attacks like phishing, domain spoofing, and business email compromise (BEC).

How does email work?

Email messages are sent from software programs and web browsers, collectively referred to as email ‘clients.’ Individual messages are routed through multiple servers before they reach the recipient’s email server, similar to the way a traditional letter might travel through several post offices before it reaches its recipient’s mailbox.

Once an email message has been sent, it follows several steps to its final destination:

1. The sender’s mail server, also called a Mail Transfer Agent (MTA), initiates a Simple Mail Transfer Protocol (SMTP) connection.
2. The SMTP checks the email envelope data — the text that tells the server where to send a message — for the recipient’s email address, then uses the Domain Name System (DNS) to translate the domain name into an IP address.
3. The SMTP looks for a mail exchange (MX) server associated with the recipient’s domain name. If one exists, the email is forwarded to the recipient’s mail server.
4. The email is stored on the recipient’s mail server and may be accessed via the Post Office Protocol (POP)* or Internet Message Access Protocol (IMAP). These two protocols function slightly differently: POP downloads the email to the recipient’s device and deletes it from the mail server, while IMAP stores the email within the email client, allowing the recipient to access it from any connected device.
   • The ‘Date’ field contains the date the email is sent. This is a mandatory header field.
   • The ‘From’ field contains the email address of the sender. If the email address is associated with a display name, that may be shown in this field as well. This is also a mandatory header field.
   • The ‘To’ field contains the email address of the recipient. If the email address is associated with a display name, that may be shown in this field as well.
   • The ‘Subject’ field contains any contextual information about the message the sender wants to include. It is displayed as a separate line above the body of an email.
   • The ‘Cc’ (carbon copy) field allows the sender to send a copy of the email to additional recipients. The recipients marked in the ‘To’ field can see the email address(es) listed in the ‘Cc’ field.
   • The ‘Bcc’ (blind carbon copy) field allows the sender to send a copy of the email to additional recipients. The recipients marked in the ‘To’ field cannot see the email address(es) listed in the ‘Bcc’ field.
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      1. The ‘Date’ field contains the date the email is sent. This is a mandatory header field.
      2. The ‘From’ field contains the email address of the sender. If the email address is associated with a display name, that may be shown in this field as well. This is also a mandatory header field.
      3. The ‘To’ field contains the email address of the recipient. If the email address is associated with a display name, that may be shown in this field as well.
      4. The ‘Subject’ field contains any contextual information about the message the sender wants to include. It is displayed as a separate line above the body of an email.
      5. The ‘Cc’ (carbon copy) field allows the sender to send a copy of the email to additional recipients. The recipients marked in the ‘To’ field can see the email address(es) listed in the ‘Cc’ field.
      6. The ‘Bcc’ (blind carbon copy) field allows the sender to send a copy of the email to additional recipients. The recipients marked in the ‘To’ field cannot see the email address(es) listed in the ‘Bcc’ field