Tuesday, 16 Jul 2024

What are Email Protocols (POP3, SMTP, and IMAP) and their default ports?

Email is an essential part of our daily lives, enabling efficient communication for both business and personal purposes. Behind the scenes, email protocols play a crucial role in facilitating the exchange of messages between servers and clients, ensuring that our emails reach their intended recipients. In this article, we will explore the most common email protocols – POP3, IMAP, and SMTP – and their functionalities, providing you with the knowledge to choose the best configuration for your specific email needs.

Email Protocols List

Let’s start by familiarizing ourselves with the standard email protocol list, consisting of:

  • SMTP (Simple Mail Transfer Protocol)
  • POP3 (Post Office Protocol version 3)
  • IMAP (Internet Message Access Protocol)

Each protocol operates differently and offers distinct services for managing your email account. Understanding their functionalities will empower you to make informed decisions regarding your email configuration.

SMTP: Simple Mail Transfer Protocol

SMTP, which stands for Simple Mail Transfer Protocol, is responsible for sending email messages. It enables communication between email clients and mail servers, facilitating the exchange of emails between computers. When you send an email, your mail client and the SMTP server establish a connection using a specific email port. Through this connection, they utilize SMTP commands and replies to process your outgoing emails, ensuring their successful delivery. Thanks to SMTP, you can send messages from various email applications using the same account.

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How the email protocol SMTP works?

POP3: Post Office Protocol version 3

POP3, short for Post Office Protocol version 3, provides access to your email inbox stored on an email server. It allows you to download and delete messages from the server. When your POP3 client connects to the mail server, it retrieves all messages from your mailbox, storing them on your local computer and deleting them from the remote server. This protocol enables you to access your messages locally, even in offline mode. Additionally, modern POP3 clients offer the option to keep a copy of your messages on the server if desired.

How email protocol POP3 works?

IMAP: Internet Message Access Protocol

The Internet Message Access Protocol (IMAP) allows you to access and manage your email messages directly on the email server. With IMAP, you can manipulate folders, permanently delete messages, and efficiently search through your emails. It also provides the ability to set or remove email flags and fetch email attributes selectively. By default, all your messages remain on the server until you delete them. IMAP supports multiple users connecting to a single mail server, making it an excellent choice for accessing your email from different locations or when multiple users manage your messages.

How the email protocol IMAP works?

Default Email Ports

To establish a connection between your email client and mail server, you need to know the IP address of the server and the corresponding port number. The Internet Assigned Numbers Authority (IANA) assigns these attributes, which define how a message should be transmitted and whether it should be encrypted. Let’s take a look at the default ports for each email protocol:

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SMTP Ports

SMTP has four available ports, each supporting a different type of encryption for email sending:

  • Port 25: This port is used for sending messages in plain text. However, many internet service providers block it due to security risks. TLS encryption may be supported if the mail server allows it.
  • Port 2525: An alternative to the default SMTP port (25), it can also be encrypted using TLS.
  • Port 587: IANA registers this as the secure SMTP port, requiring an explicit TLS connection. If the email server does not support TLS, messages will be sent in plain text.
  • Port 465: This port operates over an implicit SSL connection. If the server does not support this encryption, the operation will be aborted.

POP3 Ports

For POP3, the default port is 110, which is not encrypted. However, an encrypted port, 995, is available for secure connections using TLS/SSL.

IMAP Ports

IMAP, similar to POP3, operates on two ports:

  • Port 143: This port is the default and does not provide encryption.
  • Port 993: The secure IMAP port that works over TLS/SSL encryption.

What is the Difference between SMTP, POP3, and IMAP?

To better understand the roles of these protocols, let’s explore their differences:

Incoming vs. Outgoing Protocols

POP3 and IMAP are mail access protocols that handle incoming emails, allowing you to retrieve or access your email messages. On the other hand, SMTP is responsible for the transfer of messages from server to server or from a mail client to a server. As the outgoing protocol, it facilitates email sending from your account.

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In summary, POP3 and IMAP enable you to receive emails, while SMTP allows you to send messages.


Both IMAP and POP3 relate to email retrieval, but they function differently:

  • POP3 assumes that your email is accessed from a single application, typically downloading messages to your local computer and deleting them from the server. This reduces the space used by your email account on the web server.
  • IMAP allows simultaneous access by multiple clients, making it suitable for accessing your email from different locations or when multiple users manage your messages. With IMAP, your messages remain on the server until explicitly deleted.

To sum it up, we have explored three email protocols – SMTP, POP3, and IMAP – each with its specific port numbers and functionalities. Understanding these protocols will help you troubleshoot connectivity issues and choose alternative port numbers if needed.

Frequently Asked Questions

Coming soon…


Email protocols play a vital role in ensuring the smooth exchange of messages between servers and clients, enabling seamless communication. By familiarizing yourself with SMTP, POP3, and IMAP, you can optimize your email configuration to suit your needs. Remember to pay attention to the default ports for each protocol and consider security aspects when choosing the appropriate encryption method. If you encounter any difficulties, don’t hesitate to refer to the comprehensive documentation provided by Eireview – Extractive Industries Review.