What is POP3, SMTP and IMAP


Most likely, the majority of readers of this guide are already familiar with the most frequently used communication technology – e-mail. But have you ever thought about how it actually works? In this article we will learn how this service works, and what POP3, SMTP and IMAP are.

Step 1 – What is POP3 and which ports does it have?

POP3 (post office protocol version 3) is often used to communicate with a remote email server and download messages to a local email client and then delete it on the server, for example, Outlook , Thunderbird , Windows Mail, Mac Mail , etc. However, mail clients usually offer the choice of whether to leave copies of messages on the server or not. If you use multiple devices to send messages, it is recommended to leave this feature enabled, otherwise, on another device you will not have access to sent messages that were not stored on a remote server. It is also worth noting that POP3 is a protocol that works only in one direction, which means that data is taken from a remote server and sent to a local client.

POP3 ports, the default are as follows:

Port 110 – port without encryption

Port 995 – SSL / TLS port, also known as POP3S

Step 2 – Differences between POP3 and IMAP, and which ports does IMAP have?

IMAP (application level protocol for access to e-mail), as well as POP3, is used to receive e-mail messages to a local client, however, it has a significant difference – only e-mail headers are downloaded, the message text itself remains on the server. This communication protocol works in two directions; if changes occur on the local client, they are transmitted to the server. Recently, IMAP has become more popular, as e-mail service providers like Gmail have begun to recommend using it instead of POP3.

IMAP ports, by default are as follows:

  • Port 143 – port without encryption
  • Port 993 – SSL / TLS port, also known as IMAPS

Step 3 – SMTP, protocol for outgoing email

Simple Mail Transfer Protocol ( SMTP ) is used to communicate with a remote server and then send messages from a local client to a remote server, and ultimately to a recipient server. On your email server, this process is monitored by a special service ( MTA ). It is worth mentioning that SMTP is used exclusively for sending messages.

SMTP ports:

  • Port 25 – port without encryption
  • Port 465 – SSL / TLS port, also known as SMTPS


We hope that now you have a clear understanding of how the mail protocols work and which ports they use.In this guide, we learned what POP3, SMTP and IMAP are and what they are used for. For example, POP3 and IMAP are used for the same purpose, but they approach these tasks differently. IMAP leaves the content of the letter on the server, and POP3 downloads it to your computer. Also, we learned what standard ports from SMTP, POP3 and IMAP.

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