Despite being one of the oldest forms of digital communication, email remains essential for everything from personal conversations to business operations. But how does an email actually travel from sender to recipient — through a chain of mail servers and routing systems? In this guide, we break down each step of how email works behind the scenes — from the moment you hit “send” to the time it reaches an inbox.

1. Composing and Sending the Email

When you write an email using an email client (like Outlook, Thunderbird, or a webmail interface), the process starts with your device formatting the message — including sender, recipient, subject, body, and any attachments.

Once you click “Send,” your email client forwards the message to an outgoing mail server, typically using SMTP (Simple Mail Transfer Protocol).

2. SMTP Server Processes the Request

The email is handed off to your SMTP server, which works like a digital post office. It reads the recipient’s domain (the part after the @ symbol) and uses DNS (Domain Name System) to look up the correct MX (Mail Exchange) records for the destination server.

This tells your server where to deliver the message.

3. Relaying and Routing

In many cases, your SMTP server relays the email to another SMTP server closer to the recipient, especially if you’re on different email providers. These hops are fast and invisible to the user, but involve routing logic, spam checks, and sometimes greylisting.

During this process, the message can be scanned, queued, or temporarily delayed based on server load or security rules.

4. Delivery to Recipient’s Mail Server

Once the recipient’s mail server receives the email, it checks the message against its own spam filters, security policies, and user settings. If the email passes all checks, it’s stored in the user’s mailbox on the server.

The email remains on the server until the recipient opens their email client or app.

5. Retrieving the Email (POP3 or IMAP)

To read the email, the recipient’s device connects to the mail server using either:

  • POP3 (Post Office Protocol v3): Downloads the email and (usually) deletes it from the server.
  • IMAP (Internet Message Access Protocol): Syncs messages and folders between the server and the device, ideal for accessing from multiple devices.

Most modern clients use IMAP for better flexibility and real-time sync.

6. Displaying the Message

Finally, the email is rendered in the recipient’s client — including formatting, HTML, images, and any attachments. At this point, it behaves like any other digital message.

Behind the scenes, it may include metadata such as headers, IP paths, DKIM/DMARC/SPF validations, and more.

Summary: Email Delivery Flow

  • User composes and sends the email.
  • SMTP server processes the message.
  • DNS/MX records are checked to find the recipient’s server.
  • The email is routed, possibly relayed, and delivered.
  • Stored in the recipient’s mailbox.
  • Retrieved via IMAP or POP3.
  • Displayed to the end user.
  • Conclusion

Email may seem simple on the surface, but it relies on multiple complex systems working together — SMTP, DNS, mail relays, filters, and retrieval protocols. Understanding these steps helps you troubleshoot issues, optimize deliverability, and appreciate the underlying technology of everyday communication.