What is POP3?

POP3 (Post Office Protocol version 3) is an application-layer protocol used to retrieve (download) email from a mail server to a client.

In short: POP3 lets you pull messages from the server down to a computer or phone.

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#Why POP3 is needed

POP3 is used when you need to:

• retrieve messages from a mail server
• save them locally on a device
• work with mail offline

Historically POP3 was built for this scenario:

"connect → download mail → disconnect."

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#How POP3 works (simplified)

1. The mail client connects to the mail server
2. It authenticates (login/password)
3. The client requests a list of messages
4. The client downloads the messages
5. The messages are usually deleted from the server

This is POP3's key trait.

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#POP3's main trait

Messages are stored on the client, not on the server

Consequences:

• if mail was downloaded to one computer, it will no longer be on another device
• the state of messages (read / unread) does not sync

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#POP3 vs IMAP (in short)

• POP3
  • downloads messages
  • often deletes them from the server
  • convenient for a single device
• IMAP
  • messages stay on the server
  • suits multiple devices

In practice, today IMAP is used more often than POP3.

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#POP3 security

Classic POP3:

• does not encrypt data
• transfers the login and password as plain text

So people use:

• POP3S (POP3 + SSL/TLS)

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#A real-life example

POP3 is like:

• taking paper letters out of a mailbox
• carrying them home
• there are no more letters left in the box