POP Protocol vs IMAP vs SMTP – A Detailed Comparison

Electronic mail or email has become an indispensable mode of communication in our digital world today. We extensively use email for both personal and professional purposes on a daily basis. But have you ever wondered – how does an email get delivered from the sender to the recipient’s inbox?

There are three main protocols involved in the email delivery process – SMTP, POP3, and IMAP. While SMTP deals with sending an email, POP3 and IMAP handle retrieving emails on the recipient’s end. In this article, we will do a detailed comparison between the POP, IMAP, and SMTP protocols to understand how they work and what are the differences.

What is the Role of Protocols in Email Delivery?

For an email to get delivered it needs to travel through multiple servers across the internet. Protocols provide a set of rules and procedures to transfer data between the sender, recipient email servers and clients in a structured way.

Think of protocols as the standardized language that enables different systems to communicate with each other seamlessly Just like how two persons speaking the same language can understand each other, email protocols allow seamless communication between email servers, clients and other systems

Now let’s dive deeper into the three main protocols:

SMTP – The Protocol for Sending Emails

SMTP stands for Simple Mail Transfer Protocol. It establishes the procedure for outgoing mail to get transferred from the sender’s device to the recipient’s email server.

Here is a quick rundown of how SMTP works:

• The email client (such as Gmail, Outlook etc) connects to the SMTP server and initiates a handshake.

• The sender’s email client provides information about the email – who it’s coming from, who it’s addressed to, the content of the email etc.

• The SMTP server processes this information and routes the email to the recipient’s email server.

• Once the email is delivered to the recipient’s email server, the SMTP server sends a success notification to the sender’s email client.

Some key things about SMTP:

• Works on TCP port 25, 587 and 465
• Push protocol – pushes emails out for delivery
• Does not store messages on the server, just transfers them
• Uses TCP for transmission

SMTP allows your email client to communicate with your email provider’s SMTP server and push the emails out for delivery across the internet.

POP3 – The Protocol for Downloading Emails

POP or Post Office Protocol version 3 deals with retrieving emails from the server on the recipient’s end.

Here is how POP3 works:

• The email client connects to the POP3 server and authenticates itself.

• It then downloads the full content of all new emails to the client’s local storage.

• Once the emails are downloaded, the POP3 server deletes them from the server by default. However, some implementations allow leaving a copy on the server.

Some key things about POP3:

• Works on TCP port 110
• Pull protocol – pulls emails from server to client
• Downloads all new emails and deletes them from server by default
• Local storage needed to view emails offline
• Uses TCP for transmission

POP3 allows you to download emails to your local device and access them even when offline. However, emails are not synchronized across devices.

IMAP – The More Advanced Protocol

IMAP or Internet Message Access Protocol is a more advanced protocol than POP3. Just like POP3, it deals with retrieving emails but has more features.

Here is how IMAP works:

• The email client establishes a connection with the IMAP server and authenticates.

• Instead of downloading the full emails, the client first fetches only the message headers.

• User can select which emails to download fully on demand.

• Messages remain on the server even after downloading allowing synchronized access across devices.

Some key things about IMAP:

• Works on TCP port 143
• Pull protocol like POP3
• Downloads only message headers first, then full message on-demand
• Leaves emails on server allowing synchronized access
• More features for organizing emails in folders
• Uses TCP for transmission

The main difference between POP3 and IMAP is that IMAP allows two-way synchronization and leaves your inbox online while POP3 just downloads it to your local machine.

POP vs IMAP vs SMTP – A Quick Comparison

This summarizes the main purposes and features of the POP, IMAP and SMTP protocols. While SMTP handles sending emails, POP and IMAP deal with retrieving them on the recipient’s end. IMAP is more advanced allowing two-way synchronization and managing emails in folders.

How do POP3, IMAP and SMTP Work Together?

Now that we have understood what each protocol does, let’s see how they work together for end-to-end email delivery:

1. The sender composes an email and hits send in their email client such as Gmail or Outlook.

2. The email client uses SMTP to transfer the email from the sender’s device to their email server.

3. The sender’s email server uses SMTP to relay the email over the internet to the recipient’s email server.

4. The recipient’s email server receives the email and stores it ready for access by the recipient.

5. When the recipient opens their email client, it uses either POP3 or IMAP to retrieve the emails from the server.

6. With POP3, emails are downloaded completely and deleted from the server. With IMAP, they remain on the server in sync across devices.

• SMTP handles the sending or push function
• POP3 and IMAP handle the receiving or pull function

SMTP transfers emails between mail servers while POP3/IMAP allow clients to access their inboxes from the server.

Key Differences Between POP3 and IMAP

While both POP3 and IMAP deal with retrieving emails, there are some key differences between the two:

• Access: POP3 downloads all emails to one device while IMAP allows access from multiple devices.

• Storage: POP3 deletes emails from server after download while IMAP keeps them on server.

• Synchronization: No sync across devices with POP3 but IMAP maintain synchronization.

• Manageability: IMAP allows creating, deleting, organizing folders. POP3 has limited capabilities.

• Performance: POP3 is faster at downloading emails while IMAP downloads partial content.

• Security: IMAP uses full encryption while POP3 can optionally use encryption.

So which one should you use? Here are some recommendations:

• If you will access emails mainly from one device, use POP3.

• If you need to access your inbox from multiple devices, use IMAP.

• If you need advanced email organization and management, use IMAP.

• If you need offline access to your emails, use POP3.

Real World Analogy for the 3 Protocols

Here is a real world analogy to understand the roles of SMTP, POP3 and IMAP:

• SMTP is like the Postal Service that picks up mail from your mailbox and delivers it across the country to the recipient’s mailbox.

• POP3 is like you going to your mailbox, collecting all the mail and taking it home where you can read it even without an internet connection. But then the mail is removed from your mailbox.

• IMAP is like accessing your mailbox online from home. You can selectively read some letters online as needed without having to take all the mail home. The mail remains in your mailbox for synchronized access.

Summary

• SMTP handles the sending or pushing of emails from clients to servers and between servers.

• POP3 and IMAP deal with retrieving or pulling emails from the server to the client inbox.

• POP3 downloads all emails and removes them from server while IMAP keeps them on server for synchronized access.

• IMAP has more advanced features for search, organization, multi-folder management compared to POP3.

• Understanding the difference between POP, IMAP and SMTP helps explain how your emails make their way into your inbox everyday.