What Is Email? Email Definition

To continue the postal system analogy, imagine that Alice writes a thank-you letter to Bob. She delivers the letter to the postal company (MTA), which takes it to the post office to be sorted. At the post office, the processing clerk (SMTP) checks the address written on the envelope. If the address appears to be correctly written and corresponds to a location that can receive mail (MX server), another mail carrier delivers the letter to Bob’s mailbox. After receiving the mail, Bob may keep the note in his desk drawer, where he can only access it at that location (POP), or put it in his pocket to read anywhere (IMAP).

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* The current version of the POP protocol is called POP3.

What Are the Parts of an Email?

An individual email consists of three core components: an SMTP envelope, a header, and a body.

SMTP

The SMTP “envelope” is the data exchanged between servers during the email delivery process. It consists of the sender’s email address and the recipient’s email address. This envelope data tells the mail server where to send the message, just as a mail carrier refers to the address on an envelope in order to deliver a letter to the correct location. During the email delivery process, this envelope is discarded and replaced each time the email is transferred to a different server.

Header

Like the SMTP envelope, the email header provides important information about the sender and recipient. In most cases, the address matches the information provided in the SMTP envelope, but this may not always be the case. For example, a spoofed sender may hide the true source of the message by using a legitimate email address in the email header. Since the recipient only sees the email header and body – and not the envelope data – they may not know that the message is malicious.

The header may also contain a number of optional fields that allow the recipient to reply to, forward, categorize, archive, or delete the email. Other header fields include:

1. 1. • The “Date” field contains the date the email was sent. This is a mandatory header field.
      • The “From” field contains the sender’s email address. If the email address is associated with a display name, that may also be shown in this field. This is also a mandatory header field.
      • The “To” field contains the recipient’s email address. If the email address is associated with a display name, that may also be shown in this field.
      • The “Subject” field contains any contextual information about the message that the sender wants to include. It is displayed as a separate line above the email body text.
      • The “CC” (Carbon Copy) field allows the sender to send a copy of the email to additional recipients. The recipients specified 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 specified in the “To” field cannot see the email address(es) listed in the “BCC” field.

Body

The email body contains any information the sender wishes to send: text and/or images and/or links and/or videos and/or other file attachments, provided they do not exceed the email client’s size restrictions. Alternatively, an email can be sent with no information in the body field.

Depending on the options provided by the email client, the email body text can be formatted in plain text or HTML format. Plain text emails contain no special formatting (such as non-black font colors) or multimedia (such as images). They are compatible with all devices and email clients. HTML-formatted emails allow for formatting and multimedia within the body field, although some HTML elements may be flagged as spam by email filtering systems or may not render correctly on incompatible devices or clients.

What is an Email Client?

An email client is a software program or web application* that enables users to send, receive, and store email messages. Common email programs include Outlook, Gmail, and Apple Mail.

Both software-based and web-based email clients have advantages and disadvantages. Desktop email clients often come with more robust security capabilities, simplify email management across multiple accounts, provide offline access, and allow users to back up their email messages to their own computers. In contrast, web-based clients are typically cheaper and easier to access – users can log into their accounts from any web browser – but they rely on an internet connection and can be more vulnerable to cyberattacks.

* Originally, “email” referred to desktop email clients and “webmail” referred to web-based email clients. Today, the term “email” encompasses both systems.

What is an Email Address?

An email address is a unique string of characters that identifies an email account, or “mailbox”, where messages can be sent and received. Email addresses are formatted in three distinct parts: a local part, an “@” symbol, and a domain.

For example, in the email address example@ezznology.com, “example” refers to the local part and “ezznology.com” refers to the domain.

Think of addressing a letter: the domain refers to the city where the recipient lives, while the local part specifies the street address and house number where the message can be received.

Local Part

The local part tells the server the final destination of the email message. It may include a combination of letters, numbers, and certain punctuation marks (such as underscores). The maximum character count for an email address (including both the local part and domain) is 320, although the recommended length is capped at a maximum of 254 characters.

Domain

The domain may be a domain name, such as example.com, or an IP address, such as 192.0.2.0. In the former case, SMTP uses DNS to translate the domain name into its corresponding IP address before delivering the message to the next server.

Like the local part, the domain must also comply with certain formatting requirements set by the Internet Engineering Task Force (IETF). Valid domain names may include a combination of uppercase and lowercase letters, numbers, and hyphens. An email address can also be formatted using an IP address enclosed in brackets instead of a domain name, though this is rare. The permitted character count for a domain name is 63.

Is Email Secure?

Although email is often used to exchange sensitive information, it is not a secure system by design. This makes it an attractive target for attackers, who may intercept an unencrypted message, deploy malware, or impersonate legitimate organizations. Other email security threats include social engineering, domain spoofing, ransomware, spam, and more.

One of the most significant vulnerabilities of email is its lack of built-in encryption, which makes the contents of an email visible to any unauthorized party that may intercept or otherwise gain access to the message.

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In an attempt to make email more secure, many email clients offer one of two core encryption capabilities: Transport Layer Security encryption (or “TLS encryption“) and end-to-end encryption (or “E2EE”). During TLS encryption, messages are encrypted in transit (from user to server or server to user), and the email service provider retains possession of the private key used to set up this encryption. Therefore, the email service provider can view the unencrypted contents of the email. During end-to-end encryption (from user to user), messages can only be decrypted by the email’s sender and recipient.