Post Office Protocol Version 3 (POP3): Complete guide

Post Office Protocol Version 3 (POP3): Complete guide

Curious how emails actually get from a server to your inbox? While SMTP handles sending your messages, there's another protocol working behind the scenes to help you receive them: POP3.

POP3 (Post Office Protocol version 3) might sound intimidating, but it's one of the fundamental building blocks that makes email work. If you've ever set up an email client or troubleshooted connection issues, you've probably encountered POP3 settings, even if you weren't quite sure what they meant.

POP3 is a lot like a digital postal worker. Just as someone at the post office collects your physical mail and delivers it to your mailbox, POP3 grabs your emails from a server and downloads them to your device. But that's just scratching the surface.

Below, we’ll walk you through how POP3 works, what ports it uses, and why it matters for your email.

What is POP3?

POP3 is the third version of the Post Office Protocol—a standard mail protocol that downloads emails from a server to your local device. It retrieves your messages and brings them straight to your inbox.

Here’s what’s happening:

• Mail retrieval: POP3's main job is fetching emails from your mail server and downloading them to your device: like your computer, phone, or tablet.

• Local storage: Once POP3 downloads your messages, they typically get removed from the server. This means you can read your emails offline, and they only take up space on your device, not the server.

• One-way download: POP3 is a one-direction protocol. It downloads emails to one device and usually deletes them from the server, making it ideal for users who primarily check email from a single device.

Think about sending a physical letter. SMTP (Simple Mail Transfer Protocol) is like the postal service that moves your letter from post office to post office, while POP3 is the mail carrier who takes it from the local post office and puts it in your mailbox.

Here's how it works:

1. Someone sends you an email

2. SMTP delivers it to your email server

3. Your email client connects to the server using POP3

4. POP3 downloads the email to your device

5. You can now read your message (even without an internet connection)

POP3 isn't the only email protocol out there, though. It's actually part of a larger family of protocols that make email possible:

• SMTP: Handles sending emails between servers

• IMAP: Syncs emails across multiple devices, keeping them on the server

• POP3: Downloads emails to a single device, typically removing them from the server

How POP3 works

This entire sequence typically happens in seconds. It runs seamlessly in the background while you check your inbox. It's this efficiency and simplicity that has kept POP3 relevant in modern email systems (despite newer alternatives like IMAP).

1. Making the connection

Your email client initiates a TCP connection with your mail server. POP3 uses specific ports for this connection, typically port 110 for standard connections or port 995 for secure SSL/TLS connections.

2. Authentication phase

Before any data transfer can occur, your client needs to verify its access rights through a simple authentication sequence:

• Client transmits username

• Server acknowledges receipt

• Client sends password

• Server validates credentials

3. Transaction phase

Once authenticated, your client can execute a few core commands:

• LIST: Retrieves message numbers and sizes

• RETR: Downloads specific messages

• DELE: Marks messages for deletion

• STAT: Checks message status

These commands form the backbone of POP3's functionality to enable precise control over email retrieval.

4. Download process

During this phase, your client downloads the actual message content. POP3 transfers the raw message data to your local device, where your email client can then parse and display it.

5. Update and cleanup

After successful download, the protocol:

• Marks retrieved messages for deletion

• Removes them from the server (if configured to do so)

• Prepares to end the session

6. Session termination

The process ends with a QUIT command from your client. The server acknowledges this command, processes any pending deletions, and closes the connection.

POP3 ports and numbers

POP3 uses just a few standard ports, but knowing which one to use (and when) can prevent some connection headaches.

Standard port (110) 

Port 110 is POP3's default, unencrypted port. While it's still widely supported, it sends data in plain text, and that makes it vulnerable to potential security risks. You'll typically only see this port used in legacy systems or internal networks where security isn't a primary concern.

Secure port (995) 

Port 995 is the secure, encrypted version of POP3 that uses SSL/TLS. This is the port you'll want to use in most cases. It provides the same functionality as port 110 but with added security layers that protect your login credentials and email content.

Alternative ports

Some email providers and organizations use custom ports for POP3 access. This is less common, but you might encounter alternatives like:

• Port 1939: Used by some providers for non-standard implementations.

• Port 2110: Sometimes used for alternative POP3 services.

• Port 2995: An alternative secure port used by some systems.

Ultimately, use port 995 unless you have a specific reason not to. If you're setting up a new email client or troubleshooting connection issues, start with port 995. Only fall back to port 110 if you're working with legacy systems or your provider specifically requires it.

POP3 in modern email clients

IMAP might be the default choice for many modern email setups, but POP3 can be a great option when you want local email storage and don't need multi-device sync. Here’s how POP3 works with today's most popular email clients.

Gmail POP3 settings

Gmail offers POP3 support with these settings:

• Server name: pop.gmail.com

• Port: 995 (SSL required)

• Username: Your full Gmail address

• Authentication: Password or app-specific password if using 2FA

Gmail's implementation lets you keep server copies of retrieved messages and offers flexible configuration options through your account settings.

Common email clients

Different email clients handle POP3 in their own ways:

• Outlook: Provides streamlined POP3 setup with automatic configuration for major providers. Includes options for leaving messages on the server and managing download schedules.

• Apple Mail: Offers simple POP3 configuration with built-in support for most email services. Includes features like partial message download and custom connection settings.

• Thunderbird: Gives users granular control over POP3 settings that include detailed server configurations and flexible message handling rules.

How to set up POP3 accounts

Most modern clients follow a similar setup process:

1. Select "Add Account" or similar option

2. Choose POP3 as your account type

3. Enter your email address and password

4. Let auto-discovery find your settings or enter them manually

5. Configure download and storage options

6. Test the connection

Get started with POP3

Ready to get started with POP3? Here's how:

• Review your needs: Consider your email habits, storage requirements, and device usage patterns.

• Choose your ports: Opt for port 995 with SSL/TLS for secure communications.

• Configure your client: Use the settings we've covered to set up your email client correctly.

• Test your setup: Verify everything works as expected before relying on it.

Getting your email configuration right is non-negotiable for smooth, secure communications—and that's where we come in. Twilio SendGrid gives you the tools and expertise to implement strong email solutions for your business.

Want to learn more about email protocols, deliverability, and best practices? Sign up for a free Twilio SendGrid account and get access to our comprehensive documentation, expert support, and powerful email tools.