Differences between POP3 and IMAP

Computer Engineering Computer Network MCA

IMAP and POP3 are the most widely used standard protocol for email retrieval. Both these protocols are supported by almost all current email clients and servers. Go through this article to find out more about POP3 and IMAP, how they function, and what are the major differences between these two protocols.

What is POP3?

POP3 (or Post Office Protocol Version 3) is an application layer protocol used by email clients to retrieve email messages from mail servers over TCP/IP network. POP was designed to move the messages from server to local disk but version 3 has the option of leaving a copy on the server

POP3 is a very simple protocol to implement but that limits its usage. For example, POP3 supports only one mail server for each mailbox. It has now has been made obsolete by modern protocols like IMAP.

What is IMAP?

The Internet Message Access Protocol (IMAP) is an Internet standard protocol for retrieving email messages from a mail server via a TCP/IP connection by email clients. RFC 3501 is the standard that defines IMAP.

Because IMAP was created with the purpose of allowing many email clients to handle an email box simultaneously, clients typically leave messages on the server until the user explicitly deletes them. The port number 143 is usually used by an IMAP server. The port number 993 is given to IMAP via SSL/TLS.

IMAP is designed to retrieve messages from multiple mail servers and consolidate them all in the user’s mailbox. A typical example is a corporate client handling multiple corporate accounts through a local mailbox located on her system.

All modern email clients and servers like Gmail, Outlook and Yahoo Mail support IMAP or POP3 protocol. Following are some of the advantages that IMAP offers over POP3 −

Faster response time than POP3
Multiple mail clients connected to a single mailbox simultaneously
Keep track of message state like read, deleted, starred, replied, etc.
Search for messages on the server

POP3 Vs IMAP

Read through this section to understand the way POP3 and IMPAP function so that you can easily differentiate these two protocols.

Modes of Connection and Disconnection

In POP, clients connect to the e-mail server briefly, only for as long as it takes to download fresh messages. On the other hand, clients who utilize IMAP4 frequently keep connected as long as the user interface is open and download message content as needed. This IMAP4 use pattern might result in quicker response times for users with a large number of messages.

Several Clients at the Same Time

The POP protocol requires that a client who is connected to the mailbox is the only client connected at that time. The IMAP protocol, on the other hand, allows many clients to access the mailbox at the same time and includes methods for clients to detect changes made to the mailbox by other, concurrently connected clients.

Partial Fetch and Access to MIME Message Components

Typically, all Internet e-mail is sent in MIME format, which allows messages to have a tree structure with leaf nodes representing single part content types and non-leaf nodes representing multipart content types. Clients can obtain any of the various MIME pieces independently, as well as sections of individual parts or the full message, using the IMAP4 protocol.

These techniques enable clients to obtain the text component of a message without retrieving any associated files, as well as to stream content while it is being retrieved.

Information about the Current Status of the Message

Clients can maintain a track of message state using flags specified in the IMAP4 protocol, such as whether the message has been read, replied to, or deleted. These flags are kept on the server, allowing many clients to use the same mailbox at various times to identify state changes made by other clients.

POP does not provide a method for clients to save such state information on the server. State information such as whether a message has been accessed cannot be synchronized across clients if a single user visits a mailbox with two separate POP clients (at different times).

Both pre-set system flags and client-defined keywords are supported by the IMAP4 protocol. System flags give information about the current condition of the system, such as whether a message has been read. Keywords allow messages to be tagged with one or more tags, the meaning of which is defined by the client. Keywords aren't supported by all IMAP servers.

Multiple Mailbox

When using IMAP4, clients may create mailboxes on the server (which are frequently displayed to the user as folders), change them, remove them, and copy messages between them. Servers may now give access to shared and public files, thanks to the capability for numerous mailboxes on the server. In order to control access privileges, IMAP4's Access Control List (ACL) Extension can be utilized (RFC 4314).

Searches on the server

IMAP4 allows a client to request that the server looks for messages that satisfy a set of criteria. This technique prevents clients from having to download every message in their inbox in order to do these searches.

Built-in Extension Mechanism

IMAP4 offers an explicit method for extension, emulating the experience of earlier Internet protocols. Many IMAP4 protocol modifications have been developed and are in widespread usage. IMAP2bis lacked an extension mechanism, although RFC 2449 now defines one for POP.

IMAP is Complex

In spite of the fact that IMAP fixes many of the problems with POP, it brings a new level of complexity. When several clients access the same mailbox at the same time, server-side solutions such as Mail directory or database backends compensate for most of this complexity.

Critics have criticized the IMAP specification for not being rigorous enough, and for enabling behaviors that essentially invalidate its utility. When a server stores a message, it assigns each message an "id" that allows clients to recognize messages they've seen before

Difference between POP3 and IMAP

The following table highlights the key differences between POP3 and IMAP.

Key	POP3	IMAP
Full Form	POP3 stands for Post Office Protocol 3	IMAP stands for Internet Message Access Protocol.
Complexity	POP3 is simple and only mails can be downloaded from your inbox to local computer.	IMAP is complex and allows to see all the folders on the mail server.
Ports	POP3 listens on 110 and POP with SSL, POP3DS listens on 995 port.	IMAP listens on 143 and IMAP with SSL, IMAPDS listens on 993 port
Multiaccess	POP3 supports single device to access the mail at a time.	IMAP supports multiple devices which can access the mail at a time.
Download	In POP3, mail to be downloaded first then can be read.	In IMAP, mail can be partially read before complete download.
Mail Organize	Mails cannot be organized on mail server using POP3.	IMAP allows to organize mails on mail server.
Update Email	Mails cannot be created/updated/deleted on mail server using POP3.	IMAP allows to create/update/delete mails on mail server.
Search Content	Mail content cannot be searched on mail server using POP3. To search, mail to be downloaded first.	Mail content can be searched on mail server using IMAP.
Download	All message are downloaded at once.	Mail message header can be previewed before a message is to be downloaded.
Change	Using local email software, a mail can be updated.	A mail can be updated via a web interface or email software.

Conclusion

From the above discussion, we can conclude that POP3 and IMAP are the most popular email protocols used worldwide. Both POP3 and IMAP are Message Accessing Agents which are widely used to retrieve messages from a mail server to receiver systems. Both the protocols help in setting SPAM and virus filters.