Understanding POP3, IMAP & SMTP

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email protocols
email protocols

Introduction

Probably all of you are already familiar with the most used communication technology – email. But have you ever questioned yourself how it actually works? In this article, we will learn what drives this service.

Table of Contents

  • Step 1 — What is POP3 and what are POP3 Ports?
  • Step 2 — What’s the difference between POP3 and IMAP and what are IMAP Ports?
  • Step 3 — SMTP for outgoing email communication
  • Conclusion

Step 1 — What is POP3 and what are POP3 Ports?

POP3 (Post Office Protocol version 3) is used to communicate with the remote email server and download the emails to a local email client like Outlook, Thunderbird, Windows Mail, Mac Mail, etc. Usually, an email client will have an option whether to leave copies of the downloaded emails on the server or not. If you are accessing the same email account from different devices, it’s recommended to keep remote copies as otherwise, your second device will not download any emails if the first one already deleted them. It is also worth mentioning that POP3 is a one-way communication protocol, which means that data is pulled from the remote server and sent to the local client.

By default, POP3 ports are:

  • Port 110 – non-encrypted port
  • Port 995 – SSL/TLS port, also known as POP3S

Step 2 — What’s the difference between POP3 and IMAP and what are IMAP Ports?

IMAP (Internet Message Access Protocol) like POP3 is also used for retrieving emails to local email clients, however, it has a major difference – only email headers are downloaded, actual email message contents are left on the server. This is a two-way communication protocol as changes made on the email client are transmitted to the server. Lately, this protocol gained more popularity as email provider giants, like Gmail, recommend using IMAP instead of POP3.

Default IMAP ports:

  • Port 143 – non-encrypted port
  • Port 993 – SSL/TLS port, also known as IMAPS

Step 3 — SMTP for outgoing email communication

Simple Mail Transfer Protocol (SMTP) is used to communicate with the remote server in order to send the email from a local client to the remote server and eventually to the recipient’s email server. This process is controlled by Mail Transfer Agent (MTA) on your email server. Also, SMTP is used solely to send emails.

SMTP ports:

  • Port 25 – non-encrypted port
  • Port 465 – SSL/TLS port, also known as SMTPS

Conclusion

We hope that now you have a better understanding of email service and what ports it uses. We have learned that POP3 and IMAP are intended for the same purpose, but have a different approach with IMAP leaving email content on the server and POP3 downloading it all to your computer. We have also learned what are default SMTP, POP3 and IMAP ports.

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