SMTP, IMAP, POP3 differences

SMTP, IMAP and POP3: A brief overview of their differences

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People send and receive billions of emails each day, but most of us don’t understand the internal processes enabling this massive exchange of information. The email technology is powered by specific communication protocols that have emerged back in the 1980s. SMTP, IMAP, and POP3 are the three main protocols that enable people to send electronic mail, and this article will explain their functions and differences.

What Are Protocols?

Protocols are just collections of standard rules that allow computers to communicate with each other. Two computers that support the same protocol can exchange information seamlessly despite having different manufacturers, operating systems and software programs.

SMTP, IMAP, and POP3 all work as a series of commands and responses sent and received by email client and server programs. They are text-based, which means a human may examine this exchange directly to see what’s happening.

How Are Emails Exchanged

A basic email exchange involves three different entities:

  1. The sender
  2. The recipient
  3. The mail server

The message first goes from the sender’s email client to their mail server, which then transfers the email to that of the recipient. The message resides in the receiving server’s mailbox until the addressee decides to check for new messages.

SMTP, IMAP, and POP are the protocols guiding the message in transit. The journey goes like this:

1. The sender’s email client connects to their assigned SMTP server

2. The server validates the message, then transmits it to the recipient’s SMTP server. To do this, it first queries the Domain Name System (DNS) for the IP address of the recipient’s server.

3. The receiving SMTP server checks if the message is acceptable. If everything’s ok, it puts it into the addressee’s mailbox, where the recipient can access it.

What Are SMTP, IMAP, And POP3?


The acronym stands for Simple Mail Transfer Protocol. This is the standard protocol for transferring emails to the server or between servers. When you hit the send button, you activate a connection between your email client program and your SMTP server. Your server then finds that of the recipient and transfers the email. Both these exchanges are done using the SMTP protocol.

The route for a given email may be more complex. In some cases, it might require one or more intermediate servers to get from the sender to the recipient. Such intermediate servers are called relays, and they also use the same SMTP protocol.


This abbreviation stands for Internet Message Access Protocol. It is a popular protocol for retrieving emails from an SMTP server. As opposed to SMTP, where the sender party always initiates the connection, IMAP is used to fetch messages from a user’s mailbox on the server to their laptop or mobile.

After fetching your email via IMAP, it still remains on the server so that you can read the same email on another device. The message list is displayed immediately, but the message itself doesn’t download to your computer until you click on it, which ensures a faster connection.


POP stands for Post Office Protocol. The number “3” here refers to the current revision. It is yet another popular protocol for retrieving messages, similar to IMAP. POP3 is older than IMAP and lacks certain features, but it is still used, mostly due to its simplicity.

The main difference between POP3 and IMAP is that IMAP makes a local copy of the message, leaving the original on the server, while POP3 defaults to downloading the message immediately and then deleting it from the server.


The three protocols we’ve told you about play an essential role in delivering emails. Emails often take just a few seconds to send, and these protocols work within that short time to ensure the emails are delivered. To give you a recap:

  • SMTP sends the message
  • IMAP and POP3 both retrieve the message to the recipient’s computer, the former being more advanced.

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