Email Basics: What Is an Email Server?

Melanie Balke
April 15, 2024

An email server is the heart of all email marketing.

These massive operations handle the delivery and dispatch of the world’s countless email messages. Think of them as digital postal systems. They process outbound messages and funnel them down the system until they reach the appropriate destination.

How Emails Get Delivered

An email app badge. "Email Basics: Internet Protocol for Emails."

Whenever you check or send an email, you’re using an email client (formally, a “mail user agent” or “message user agent”). Once little more than massive blocks of plain-text information, email clients have evolved into user-friendly ways to manage your digital mailbox.

While some places may use proprietary email clients, most are built upon one of a handful of influential services. The most popular options are Apple Mail, Google’s Gmail, Microsoft Outlook, and Yahoo Mail.

In the postal system analogy, an email client is your mailbox. It lets you receive messages and hosts outbound correspondence.

1. Someone Sends an Email Message

All electronic mail begins the same way, regardless of its server status. Someone writes an email and hits the “send” button.

All outbound mail is sent from the user’s email client through their MUA (and that’s “mail user agent,” not “makeup artist”). This action is the digital equivalent of sticking a letter in your mailbox and flipping the red flag or dropping a package at your local post office.

Functionally, a sent email creates outgoing mail requests and enlists the aid of an email client. It’s even tucked neatly into a data package, “email envelope data.”

2. The Outbound Mail System Processes the Mail

Next, those email messages move to the “sorting center.”

Of course, electronic mail doesn’t need to be put on a truck or passed along conveyor belts. Instead, it’s passed to an email client, which runs the content through a Simple Mail Transfer Protocol (SMTP). Nonetheless, that computer system serves the same purpose as a physical mail facility.

The Domain Name System (DNS) is an email’s final destination. Outgoing mail servers parse that data from the recipient’s email address. The first half of an address — before the “@” — is your individual mailbox, while the second half is your account’s server.

For example, assume your email address is If you think of an email server as a postal system, this is your address. Your domain name — “” — is like a street. Your individual account — “Melanie” — is your house number. You don’t technically occupy all of the server space; instead, like your house, your email address occupies a spot within a larger computer system.

3. An Inbound Mail Transfer Agent Sorts Emails

From there, your electronic mail moves to an MTA. This software is like your local post office. It handles incoming mail and organizes it into easy-to-handle parcels for delivery drivers.

Of course, there’s a more technical breakdown for this process. When an outgoing mail server receives content, it contacts a mail exchange (MX) registry. That database houses a list of domains and servers. In mere seconds, the server locates the appropriate MTA by the recipient’s IP address. Should the process fail to return a valid result, the server returns an alert to the sender.

Generally, a mail server works by breaking larger content into smaller pieces. It finds the overarching server, matches the domain name, and narrows options down to the recipient’s IP address.

4. A Mail Delivery Agent (MDA) Delivers the Content

We’re not finished yet! Now, a mail delivery agent (MDA) delivers the email message to the appropriate email client, filling the role of a local deliveryperson.

Some mail servers use multiple layers of protection, necessitating several security checks before the email envelope data lands in the email client. Others are simple, requiring little more than sorting within the user’s mail app.

5. The Recipient Retrieves the Email

Finally, the recipient opens the email.

Email servers handle content by passing it through Internet Message Access Protocol (IMAP) or Post Office Protocol version 3 (POP3) to convert raw data to legible information.

An IMAP server hosts content on a network, enabling account access on multiple devices. Most popular consumer-grade email services use Internet Message Access Protocol, as the process is more flexible and user-friendly. However, as with anything on a network, an IMAP server is susceptible to cybersecurity threats.

Conversely, a Post Office Protocol inbox usually hosts content on an individual device and deletes the network files. (Although some give users the option to leave content on the network server.) This process essentially means the server is a computer, not a network. POP3 is an ideal solution for users with limited server space or high-security needs. However, traditional POP3 email inboxes can only be accessed through a single device.

What Does That Mean?

Now, that’s a lot of technical jargon.

It’s easy to feel overwhelmed by the specifics of email servers, but don’t worry! This blog post isn’t finished!

I want to explain things step-by-step and break down those strange technical terms — so I’ll start at the top! Hopefully, these definitions will help you better understand the big question: What is an email server?

What Is a Mail User Agent/Message User Agent (MUA)?

Also known as email clients, MUAs are your quintessential mail application. They handle the display of your precious emails and do the most visible work in the mail server software chain.

The specifics of consumer mail clients vary widely. Some have advanced capabilities, while others rely on simple layouts. The under-the-hood technology powering a mail client determines its capabilities. Nonetheless, all MUAs handle and display at least two content “blocks”: the header and subject line. Additional “blocks” include images, interactive content, and preview text.

What Is a Simple Mail Transfer Protocol (SMTP)?

Beyond its function as a delivery agent, a modern Simple Mail Transfer Protocol (SMTP) server manages and monitors email content. Think of it as a safety official for the email delivery process.

Bare-bones SMTP does little more than access inboxes and confirm addresses. However, most modern SMTP measures include additional programming for spam filtering and moderate data protection via encryption.

What Is the Internet Message Access Protocol?

Like SMTP, IMAP (and, by extension, POP3) supports modern online communication. It can decrypt sensitive information and handle its final delivery to the user’s inbox. Most personal accounts use massive IMAP servers, although businesses often have dedicated, private servers.

There are also alternatives to IMAP, including POP3 and several proprietary mail client extensions.

Learn More About Emails

So, what is an email server?

Contrary to what some may believe, an email server is dedicated to sending and receiving emails. It does not include email storage and access, both of which occur within an email client. Nonetheless, email servers are the basis for email communication.

At The Email Marketers, my team understands these highly technical specifics. They know how different IMAP servers handle incoming mail and how that can impact marketing performance. They even know how to set up individual servers with appropriate server settings!

Schedule a free strategy session to learn more about your own servers. You can also boost your understanding of mail server information by browsing the rest of my blog! You’ll find more than email server software. I also discuss email marketing and the digital landscape.