How does email work? Decode the mysteries with our straightforward guide

What even is email? If you’re asking this question then welcome to the exciting – and occasionally mindboggling – world of electronic communications. In this post we’re covering the basics of email and shedding light on how it works and why you should care.



What is email? Well, we know it’s a cheap, effective form of communication that is so widely used there’s an entire global infrastructure to support it. We rely on email for communications, confirmations, account security, and information sharing. In this article, we’ll demystify the workings of email, define the primary email protocols, go through some key email concepts, and explain the email communications process so you don’t get lost in email systems or caught in pesky pitfalls like spamtraps.

What is email?

Email is just something that … works. Right?

Have you ever wondered what happens when you hit that “Send” button? Once an email leaves your outbox, it embarks on a wild email odyssey, winding it’s way through a complex network of routes, servers, and protocols to finally (fingers crossed) land in the inbox.

Email (or e-mail, as you may know it) stands for electronic mail and is the cyberspace counterpart to physical mail. But think of email less like your postman putting a letter in your mailbox, and more like ye old Pony Express where a rider on horseback navigates an extreme terrain to deliver your message. Yes, email is a way to send messages to a recipient using electronic devices operating across the internet and local networks, but there are robbers on the email highways, venomous viruses, and a slew of other perils that can derail your campaigns.

The email journey

To understand how email works and the types of tools and practices that make an email’s journey easier, let’s first take a look at what that journey actually entails.

  1. First, you compose an email in your email account. This interface is powered by your email client.

  2. Your email client combines your message copy, recipient, subject line, date, and timestamp in an email header.

  3. Your email client communicates with an outgoing mail server provided by an email service provider, like Mailgun, via an email protocol.

  4. Your message is transferred via this email protocol to the sending server.

  5. The sending server communicates with your recipient’s receiving mail server, powered by their inbox service provider (ISP), with an email protocol.

  6. If your message passes muster; authentications, spam filters, etc. It is filtered to the inbox.

  7. Your recipient checks their email account, at which point their email client communicates with the receiving mail server to retrieve your email message with an email protocol.

Each transfer of your original email message at each check point throughout the journey uses an email protocol. We’ll go into more detail on email protocols in the section below, but these protocols are essentially sets of rules that define how messages are exchanged. The goal of protocols is to help standardize message transferring on a universal and global level. But, of course, there are always exceptions.

Learn more: Authentications help validate your sender identity so you don’t get flagged as a spammer, among other things. Learn which ones you need, and which ones will give you an edge with our guide.

What are email protocols?

Email protocols facilitate email sending and receiving. There are three main types of email protocols:

  • SMTP

  • IMAP

  • POP

Let’s take a look at each of these protocols below.

What is SMTP?

Simple Mail Transfer Protocol (SMTP) handles the delivery of emails. This protocol is responsible for transferring your email from your email client to an SMTP server. The server then uses SMTP protocol to authenticate your message and ferry your email to your recipient’s receiving mail server.

Learn more: Check out our guide on which SMTP port to use and how to set them up.

What is IMAP?

You’ve probably heard of SMTP and Internet Message Access Protocol (IMAP) mentioned together. In simple terms, if SMTP handles the delivery of emails, IMAP focuses on accessing emails.

Once SMTP transfers your email to your recipeint’s receiving mail server, that server stores your email message. When your recipient checks their email account, their email client uses the IMAP protocol to communicate with their mail server to retrieve your message. IMAP leaves a copy of your message on the server and retrieves a copy of it to your subscriber’s email client, where they can view your message. In other words, IMAP synchronizes all the messages on the mail server with all the messages on your subscriber’s email client.

Learn more: Check out the key differences between SMTP vs. IMAP and learn which is right for you.

What is POP?

Like IMAP, the Post Office Protocol (POP) retrieves email from a mail server. The difference between POP vs. IMAP is that while IMAP synchronizes all the messages on the mail server with all the emails in your recipient’s email client, POP only retrieves specific messages. In addition, POP doesn’t leave a copy of your email on the mail server. Think of IMAP as the POP protocol both improved and at scale.

What are other critical elements related to email?

Now that we’ve gotten the basics of email protocols out of the way, let’s go over a few more important email concepts:

  • DNS

  • MUA

  • MTA

  • MDA

Did we mention that email concepts and terms are full of acronyms? Okay, let’s try to get these four concepts straight.

What is DNS?

Domain Name Service (DNS) is a way to “map” domain names onto IP addresses. In other words, it provides a human-readable domain name like that you can enter to navigate to Mailgun’s landing page instead of a series of numbers like 192.168. 1.1. Which one would you find easier to remember?

DNS is important for email because it identifies the sender of the email message. If you use an ESP like Mailgun to send your marketing email campaigns, you might want to consider using reverse DNS (rDNS) to white-label your emails so that they state your business as the sender.

What is an MUA?

A Mail User Agent (MUA) is an email interface with which a user interacts. In other words, MUAs can be web-based or app-based email clients like Gmail, Microsoft Outlook, Yahoo, or AOL.

What is an MTA?

No, this isn’t the Metro Transit Authority. A Mail Transfer Agent (MTA) is software that transfers emails from you to your subscriber. Once you send an email from your MUA, your message is transferred to an MTA like an SMTP server via SMTP protocol.

What is an MDA?

An MTA uses the SMTP protocol to relay your message onward to a Message Delivery Agent (MDA). MDAs are also described by terms like mailbox server or receiving mail server. From here, your recipient uses the IMAP protocol to retrieve your message from the MDA to their MUA.

How does email work?

Now that we’ve memorized the acronym salad, let’s test your memory look at how email works.

SMTP flowchart

How email works:

  1. You’re interacting with your MUA, an email client like Gmail. You hit send.

  2. The SMTP protocol transfers your message to an MTA, like Mailgun’s SMTP server.

  3. The MTA authenticates your email and preps it for transfer.

  4. The MTA communicates with the MDA using the SMTP protocol and ferries your message to the MDA. Your email now waits in the receiving mail server for your subscriber to retrieve it.

  5. Your recipient uses their MUA to retrieve your email. Their MUA communicates with the MDA using the IMAP or POP protocols.

  6. Your recipient’s MUA downloads and locally stores a copy of your email. At this point, POP will delete the original message on the mail server while IMAP leaves the original email intact on the server.

Yikes. If you feel like you need a translator don’t worry, we still have to look up what some of these acronyms stand for. Fortunately, we’ve got some pro email whisperers on standby. Meet them here.

What is email deliverability?

All of the checkpoints on the email journey, the protocols, and the critical elements we’ve talked about above are part of something we call deliverability. Deliverability is just a fancy word for how do I get my message into my recipient’s inbox? There are many best practices around this that we haven’t covered here, but understanding what an email message goes through to get where it’s going is a solid start.

Learn more: Get a better understanding of email deliverability with our intro guide.

Wrapping up: Is email worth the effort?

Who would have thought that there was so much involved with sending a simple email? Getting your message out there may feel as simple as hitting send, until you take a peak behind the scenes. Once you do, you’ll see that between all of the authentications, protocols, certifications, and obstacles like spam traps, what you really need to be a good sender is a strong deliverability strategy.

Don’t worry, building your strategy doesn’t have to break your brain. Step 1: Learn more about email deliverability. This is a great place to start. Step 2: don’t be afraid to pull in the pros.

Learn about our Deliverability Services

Deliverability Services

Looking to send a high volume of emails? Our email experts can supercharge your email performance. See how we've helped companies like Lyft, Shopify, Github increase their email delivery rates to an average of 97%.

Related readings

POP vs IMAP email protocols: What's the difference?

We’ve talked about how email works and how email protocols facilitate the transfer of your emails along the way, from when you hit send to when your subscriber reads your email...

Read more

Zero inbox notes

I recently read a post by Fred Wilson about email pain. The pain being that there are too many emails to read them all and respond if...

Read more

Page views vs engagement

With the proliferation of social networks and online market places, the importance of true email integration has become more...

Read more

Popular posts

Email inbox.

Build Laravel 10 email authentication with Mailgun and Digital Ocean

When it was first released, Laravel version 5.7 added a new capability to verify user’s emails. If you’ve ever run php artisan make:auth within a Laravel app you’ll know the...

Read more

Mailgun statistics.

Sending email using the Mailgun PHP API

It’s been a while since the Mailgun PHP SDK came around, and we’ve seen lots of changes: new functionalities, new integrations built on top, new API endpoints…yet the core of PHP...

Read more

Statistics on deliverability.

Here’s everything you need to know about DNS blocklists

The word “blocklist” can almost seem like something out of a movie – a little dramatic, silly, and a little unreal. Unfortunately, in the real world, blocklists are definitely something you...

Read more

See what you can accomplish with the world's best email delivery platform. It's easy to get started.Let's get sending
CTA icon