What layer is POP3?

POP3, which stands for Post Office Protocol version 3, is an application-layer internet standard protocol used by local email clients to retrieve email from a remote mail server over a TCP/IP connection. Specifically, POP3 is commonly used for:

  • Downloading new email messages from the mail server to the local client
  • Removing/deleting email content from the server after downloading
  • Working in conjunction with SMTP for sending messages

So in summary, POP3 operates at the application layer of the OSI or TCP/IP model, enabling email clients to access email from servers.

What layer is POP3?

How Email Protocols Work

To understand where POP3 fits in, it helps to look at a typical workflow for sending and receiving emails:

  1. A user composes an email in their local email client and clicks send
  2. The email client uses SMTP (Simple Mail Transfer Protocol) to send the email over the internet to the recipient’s mail server
  3. The recipient’s mail server receives and stores the incoming email
  4. The recipient then uses a protocol like POP3 or IMAP to connect to their mail server and download new messages to their local email inbox

So in this process:

  • SMTP handles sending and routing emails across internet
  • POP3/IMAP enable the recipient to retrieve the emails from the mail server

Key Differences Between POP3 and IMAP

While POP3 and IMAP both allow accessing email from a remote server, some key differences include:


  • Emails are downloaded and deleted from the server
  • Good for occasional email access
  • Single device access


  • Keeps all messages on the server
  • Allows simultaneous multi-device access
  • Good for frequent emailing

So in summary, POP3 is good for downloading emails to one computer whereas IMAP enables accessing the same email account across multiple devices.

Where does POP3 fit in the OSI Model?

As an application layer protocol related to email delivery, POP3 fits at the application layer of the OSI model:


OSI Layer Function
Application POP3, SMTP, IMAP, HTTP
Presentation Encryption, ASCII, JPEG
Session Manages sessions and connections
Transport TCP, UDP
Network IP addresses, routing
Data Link Ethernet, MAC addressing
Physical Cables, connectors, signals

So POP3 operates at Layer 7 facilitating communication between email servers and clients.

How POP3 Works

When a local email client connects to a mail server via POP3, several steps occur:

  1. The client opens a TCP connection on port 110 of the server
  2. The client and server exchange greetings/capabilities
  3. The client provides username & password for authentication
  4. The client can then list or retrieve messages
    • Individual messages marked for deletion on server
  5. When done, the client closes TCP connection

This download and delete behavior is characteristic of POP3.

POP3 vs IMAP Technical Differences

As covered earlier, POP3 and IMAP vary in some key technical ways:


  • Uses port 110
  • Marks messages for deletion on download
  • Removes messages from server


  • Uses port 143
  • Leaves messages on server
  • Allows simultaneous connections

So in summary, POP3 typically clears messages from the mail server after download, whereas IMAP keeps them on the server allowing multi-device access.

POP3 Communication Process

The typical sequence of communication between an email client and server with POP3 is:

  1. Client opens TCP connection to server on port 110
  2. Client sends initial USER command with username
  3. Server responds confirming connection open
  4. Client sends PASS command containing password
  5. Server grants access after positive authentication
  6. Client can then issue commands to list or retrieve emails
    • Common commands: LIST, RETR, DELE
  7. When done retrieving messages, client sends QUIT to close connection

So in brief, the client authenticates, downloads messages, optionally deletes them from the server, then closes the connection.

Common POP3 Commands

POP3 uses simple text-based commands that the email client sends to the server over the TCP connection.

Some common and important ones include:

Command Description
USER Provides the username for authentication
PASS Sends the password for authentication
STAT Requests status of messages on server
LIST Lists message numbers and sizes on server
RETR Downloads/retrieves a specified message
DELE Marks particular message for deletion on server
QUIT Closes TCP connection when session done

So while limited compared to IMAP, POP3 provides essential commands for authenticating, downloading, and removing messages from the email server.

POP3 vs IMAP – A Summary Table

Feature POP3 IMAP
Internet Standard RFC 1939 (POP3) RFC 3501 (IMAP)
Port Number 110 143
Leave Messages on Server? No, deletes after download Yes
Multiple Device Access? No, downloads to one location Yes
Better For… Occasional Access Frequent Access

So in summary:

  • POP3 and IMAP operate at the application layer to enable email access
  • POP3 offers simple downloading to one client while IMAP permits advanced multi-device access

Key Takeaways

  • POP3 is an application layer protocol used to retrieve email from remote servers
  • It leverages port 110 TCP connections to authenticate and facilitate email downloads
  • Messages are typically deleted from the server after transfer via POP3
  • IMAP alternatively leaves messages on the server for multi-device access
  • Understanding differences between POP3 vs IMAP helps select optimal email protocol


In conclusion, Post Office Protocol version 3 (POP3) operates at the application layer of the internet model to deliver email retrieval capabilities. After opening a TCP connection on port 110 and authenticating with username and password, POP3 enables an email client to connect to a remote server, list and download messages, optionally delete emails from the server, and finally close the connection when finished.

While limited to single destination delivery and removal of messages after transfer, POP3 offers an efficient way to retrieve emails from a server to a local mail client or application. With candidates like IMAP also available, choosing POP3 vs IMAP depends on use case like mobility needs and server message retention requirements. By learning key details of POP3 alongside alternatives like IMAP, one can determine the best email handling solution for a particular user or organization.

Frequently Asked Questions

  1. What port does POP3 use?
    POP3 commonly uses port 110 for communication between the client and mail server.
  2. Does POP3 leave messages on the server?
    No, POP3 typically deletes messages from the mail server after downloading them to the local client, unlike IMAP which leaves copies on the server.
  3. Is POP3 end-to-end encrypted?
    No, POP3 uses TLS encryption to secure the connection, but messages are not end-to-end encrypted by default. Extra measures like PGP may be added for true end-to-end message encryption.
  4. What is a POP3 server?
    A POP3 server is specially configured mail server software on a networked computer that handles client connectivity over port 110 and supports related email retrieval commands like LIST, RETR, and DELE.
  5. Can you have multiple POP3 accounts?
    Yes, most email clients like Outlook and Thunderbird allow configuring and accessing multiple POP3 accounts under one program. The user would manage each account separately.
  6. Does Gmail support POP3?
    Yes, Gmail allows enabling POP3 access in account settings to retrieve Gmail contents from another client that supports POP3 connectivity. Messages may get deleted from the Gmail server afterward per POP3 workings.
  7. What is better, POP3 or IMAP?
    It depends on use case. POP3 offers simple one-client access while deleting old emails from the server. IMAP keeps all messages on server for access from multiple devices simultaneously. So mobility requirements help determine POP3 vs IMAP priority.
  8. How do I enable POP3 in Gmail?
    In Gmail account settings under “Forwarding and POP/IMAP”, enable “Enable POP” and select POP settings. More options exist like leaving messages accessed by POP on the server. Authentication setup in email client also needed.
  9. When would POP3 be used over IMAP?
    POP3 may be preferred if a user only accesses email from one main computer, doesn’t need advanced searching features, and wishes emails to be deleted from the Gmail server after local retrieval to one client.
  10. Can you use POP3 and IMAP at the same time?
    Technically yes, although functionality may overlap. Typically it would be one or the other handling a Gmail account, with IMAP adding more flexibility for tasks like accessing from multiple points.
  11. Does Outlook support POP3?
    Yes, Outlook has long included native support for both POP3 and IMAP email accounts. Support spans Outlook on the desktop, web, and on mobile apps.
  12. What is a POP3 email?
    A POP3 email refers to an email message downloaded from an email server to a local client using POP3. It may also refer to the actual POP3 protocol commands used behind the scenes to facilitate retrieving said message.
  13. What network port does POP3 use to check for new email?
    POP3 uses TCP network port 110 on the mail server to listen for connection requests from email client applications wishing to check for new email on the server. This allows proper routing of POP3 traffic.
  14. Can I access Yahoo Mail with POP3?
    Yes, Yahoo Mail supports POP3 access to retrieve emails into third party email clients. After enabling “Allow apps that use POP” in Forwarding settings, Yahoo will generate a unique POP server URL for configuring your specific POP email client.
  15. Does POP3 support secure connections?
    Yes. Although not encrypted by default, POP3 does support Transport Layer Security (TLS) to encrypt connections between email client and mail server. This prevents potential eavesdropping on POP3 sessions.
  16. What is a POP3 client?
    A POP3 email client is client software like Outlook or Thunderbird that supports POP3 connectivity. This allows it to connect to POP3 servers on port 110 to authenticate and then retrieve emails locally according to POP3 protocol commands.
  17. How do I find my POP3 server settings?
    To find your email account’s correct POP3 server settings, log into your email provider account’s control panel or support forums. Lookup inbound email server settings (usually under advanced options) to get hostname and port (usually port 110) to allow POP3 client connections.
  18. Can you have the same email inbox in both POP and IMAP?
    No. An email inbox would use either POP3 or IMAP protocols to sync messages, but not both simultaneously. However, one could have separate accounts or folders using POP while others leverage IMAP capabilities.
  19. What are the disadvantages of POP3?
    Disadvantages of POP3 include deleting of messages from the server after local download, lack of simultaneous multi-device access due to single endpoint delivery, limited search/organizational capabilities, and lack of native encryption.
  20. What network layer does POP3 operate at?
    POP3 operates at the Application Layer (Layer 7) of the OSI model for establishing communication between email clients and servers over a TCP/IP network. This application layer functionality enables the email retrieval capabilities that defines POP3.

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