Email, or electronic mail, is a method of exchanging digital messages over the Internet. Understanding how email works involves several components and stages.
Here is a very high-level overview:
- User Interfaces: This is what the user interacts with. Email can be accessed through webmail (like Gmail in a web browser), email clients (like Outlook or Thunderbird), or mobile email apps.
- Creation of the Message: When you compose an email, you specify the recipient, subject, and body (main content) of the message. You can also attach files.
- Sending the Message:
- When you hit “send”, the email client or webmail system communicates with the SMTP (Simple Mail Transfer Protocol) server. SMTP is used to send emails.
- The SMTP server processes the email and looks at the recipient’s email address. Using the domain (the part after ‘@’ in the email address), the server determines where to send the email.
- Routing the Message:
- The Domain Name System (DNS) is used to look up the MX (Mail Exchange) records of the recipient’s domain. This helps the sending server determine the IP address of the recipient’s email server.
- Once the correct address is found, the email is sent to the recipient’s mail server.
- Receiving the Message:
- The recipient’s email server, using protocols like POP3 (Post Office Protocol 3) or IMAP (Internet Message Access Protocol), holds the email until the recipient retrieves it.
- IMAP is more modern and versatile, allowing for emails to be synced across multiple devices. POP3, on the other hand, typically downloads the email to a single device and removes it from the server.
- Reading the Message: When the recipient checks their email:
- If using a webmail service, the email is already on the server, and the user simply views it through their web browser.
- If using an email client, the client will communicate with the recipient’s email server using IMAP or POP3 to download or sync the new messages.
- Storage: Emails can be stored on the server (common with IMAP and webmail) or on the user’s device (common with POP3). Many modern systems offer a mix, with emails stored on servers for easy access and backup, but also cached or downloaded to user devices for offline access.
- Security: Given the potential sensitivity of email content, several security measures are often employed:
- Transport Layer Security (TLS) or its predecessor Secure Sockets Layer (SSL) encrypts the connection between email servers and clients to ensure that the messages are transmitted securely.
- SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) are techniques and protocols designed to combat email spoofing and phishing.
- Additional Features: Modern email systems also provide additional features such as filtering, labelling, automated responses (out-of-office messages), and search functionalities.
Many more technical details and nuances exist in the world of email infrastructure and protocols such as Microsoft’s Hosted Exchange service.