How Do Email Protocols Work? Understanding SMTP, POP3 and IMAP


By: Drew Germyn

Categories: Guides

The first email ever was sent by a man named Roy Tomlinson in 1971. That means that email is nearly 50 years old, although its use didn’t become common until the price of computers was affordable enough for owning one to become normalised.
You might think that email has changed a lot since its introduction. Surprisingly, it’s still essentially the same as it was. The only thing that has changed dramatically is the technology behind emails.
At Localnode, we offer reliable web hosting for small businesses to ensure that our clients can send and receive emails in a timely manner. Here’s what you need to know about how email works and the differences between SMTP, POP3, and IMAP.

How Does Email Work?

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Email operates on something called a client-server system. The email client is what most people would call an email provider. Common examples include:

  • Gmail
  • Outlook
  • Hotmail
  • Apple Mail

Some of these email clients are web-based while others are built into operating systems such as Windows.
The server operates behind the scenes, receiving and sending messages. When someone sets up an email server, they configure it with the client to ensure smooth transmission of emails.

What is SMTP?

SMTP is the protocol used for nearly all email transmissions, aka sent emails. SMTP stands for Simple Mail Transport Protocol.
When you click send on an email, your client-server connects with the SMTP server that corresponds to the intended recipient’s email server. The server will likely follow two potential naming formats:


Of course, if the recipient’s domain name is something other than .com the name will change accordingly. Connecting to the recipient’s server via a port allows the email message to be sent. The ports on the sending and receiving end must match up. Most modern systems use port 587, meaning that the sending and receiving ports will both use that name. Other port options include:

  • Port 25 (historically the most common choice)
  • Port 465 (deprecated)
  • Port 2525 (non-standard)
  • A unique port number

The username and password are used to authenticate that the sender is authorised to send an email.

How Does Incoming Email Work?

Incoming email is more complex when it comes to client configurations. That’s because instead of just one option – like there is for outgoing email, there are two. The option you choose will depend upon which method your email server supports. If your server only supports one option, that’s the one you’ll use.
The two methods available are POP3 and IMAP. Let’s talk about each one.
POP3 stands for Post Office Protocol. It’s the original protocol used to collect email from a server and the most widely available option. However, it has some issues.
Because POP3 has been around since the days of dial-up connections, it transmits little data between the email client and the email server. Once the email has been transmitted, the email is deleted from the server. Using it can help free up space on the server, but that’s not as much of an issue now that so many of us have high-speed internet.
Perhaps the biggest argument against POP3 is the deletion of emails from the server. While it does free up space, it also means that emails are not recoverable if they are deleted from the machine where they were downloaded. With no back-up on the server, those emails will be gone for good if something happens to the computer where they’re stored.
IMAP stands for Internet Message Access Protocol. In some ways, it’s the reverse of POP3 because instead of downloading messages and deleting them from the server, it caches a limited number of messages for off-line access while syncing with the server to allow online access. That means that if your email client uses IMAP, you’ll be able to access your email from anywhere. It’s not device-dependent.

Should You Use POP3 or IMAP?

If you have a choice, then IMAP is going to be the preferable option most of the time. It allows for remote access to emails from any location or device.
The one exception would be if you have slow or spotty internet. For example, a rural location might benefit from using POP3 because all emails will be downloaded onto a machine and may be backed up from there.


Understanding the differences between SMPT, POP3 and IMAP will ensure that you make the best choice for your small business or personal website.
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