IMAP, POP3, SMTP - All You Need to Know About Mail Protocols

What Are Email Protocols — POP3, SMTP, and IMAP?
Alex Kachalov Alex Kachalov 31 january 2023, 21:35 1756
For beginners

When configuring an email client or application, you will encounter the terms POP, SMTP and IMAP. Which option will you choose, and why?

Don't worry if you don't yet understand these terms and how they affect your email setup. In this article you'll discover whether SMTP or IMAP is the right option for you. We’ll assist you in understanding the differences between SMTP, POP3 and IMAP.

Which Mail Protocol Is Used to Send Mail Messages to a Server?

Email protocols are rules that allow email clients and servers to exchange data. Simple Mail Transfer Protocol (SMTP) is the standard method for transferring emails between mail servers. It is the only dedicated email-sending protocol.

The protocol was initially created without security and anti-spam considerations in mind. Core SMTP specification does not require user authentication to function. Modern SMTP server applications employ certain restrictions. However, they cannot entirely eliminate unsolicited email, which may eventually reach your email server and, consequently, your inbox.

What Are POP3 And IMAP?

POP3 (Post Office Protocol version 3) is a standard protocol for retrieving email messages from a remote server. It enables the client software to download email messages to your local computer and later access them offline. POP3 is also capable of deleting messages from the server.

POP3 uses two well-known ports by default:

  • Port 110 is used for non-encrypted connection;
  • Port 995 defaults to secure connection.

Internet Message Access Protocol (IMAP) is an alternative protocol which also allows client software to access a mailbox on a remote web server. IMAP is newer, more feature-rich and also more complex to implement. Unlike POP3, it defaults to keeping the original message on the server. It has built-in support for message flags and mailbox folders, and is capable of downloading selected parts of a message. With IMAP, the same mailbox can be simultaneously accessed by multiple clients, while POP3 allows only one connection per mailbox.

By default, IMAP protocol uses one of these two ports:

  • Port 143 is the default non-encrypted IMAP port;
  • Port 993 is the port is used for a secure connection.

What Is SMTP?

The acronym SMTP stands for Simple Mail Transfer Protocol, and it's the standard protocol for sending emails. It allows you to send, relay, or forward messages from an email client (such as Microsoft Outlook) to an email server. A sender connects to an SMTP server to carry out the process of sending an email message. An email server uses the same protocol to relay messages to another server.

By default, SMTP uses these ports:

  • Port 25 is the default SMTP port for server communication; some providers may also use port 2525;
  • Ports 465 and 587 are mostly used by client software.

The Difference

Since you already know what each email protocol is capable of, you can easily see the differences between protocols. So let's review these differences.


Both POP and IMAP protocols are used to retrieve emails from an email server so that you can read it on your device. They're used by desktop email clients like Outlook, Thunderbird, Spark, Apple Mail, or something similar that you might use to connect to your mailbox. When you install and set up your email client, you’ll see which protocol your software uses.

When using webmail (such as, you don't have to worry about these email protocols because the service handles all operations for you.


IMAP and POP3 allow you to retrieve emails, while SMTP enables you to send them. You’ve got it right, your email client application needs two protocols to work properly! When setting up your software, you usually need to provide server name, port and login credentials for both.

Here’s how SMTP and IMAP/POP3 cooperate to send an email message:

  1. After you compose an email, your email client will use SMTP to transmit the message to an email server.
  2. The email server will then send the message to the recipient's email server using SMTP.
  3. If the SMTP transmission is successful, the recipient's email client will retrieve the message using IMAP or POP3 and store it in the recipient's inbox.

Summary of the SMTP, IMAP, and POP3 Email Protocols

Here's a quick summary of this blog post:

  • SMTP is the most basic email protocol. Mail servers and clients use SMTP to send and relay emails.
  • POP3 and IMAP are both used to retrieve messages from a server onto a local computer. POP3 is older and easier to implement, while IMAP is more advanced. Today most client email applications use IMAP.
  • All protocols mentioned above may use either encrypted or non-encrypted connection. Use the former to protect your privacy.

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