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Last Updated on March 19, 2023

IMAP and POP3 are the two main protocols used for email management by web hosts. Both have their benefits, yet differ in complexity. Depending on the scenario, one may be more applicable than the other, but it is important to note that the most frequently used integration in today’s servers is IMAP because of its more advanced features.


Designed by Mark Crispin, a Systems Programmer, in 1986 as a remote mailbox protocol and with the goal to permit complete management of an email box by multiple connected clients. This would then enable clients to leave messages within the server until they were explicitly marked to be deleted. This function gives IMAP the advantage of synchronisation over multiple devices. IMAP has gone through various naming schemes and known by Internet Mail Access Protocol, Interactive Mail Access Protocol and Interim Mail Access Protocol.

IMAP is used for online and offline access, possessing the ability to store messages in cache for local copies. Generally, IMAP is beneficial to most users for its ability to allow multiple clients to manage the same inbox simultaneously. This allows organisation to occur despite the location with replications that are broadcasted live to the server.

Unlike its brother protocol POP, IMAP benefits in not having to download new messages with every new connection to the server, because IMAP clients often stay connected as long as the user interface is active, offering a faster response time.

The conveniences come at a price though, because unless the client and server are being run on up-to-date hardware with optimal RAM and CPU, the frequent synchronising may cause bottlenecks from duplicate messages continually syncing between client(s) and server.

Typically, IMAP runs on server port 143 and was built around the original Xerox Lisp machines, or machines specifically made to run software written with Lisp, the second-oldest high-level programming language used for practical mathematical notation. The first iteration no longer exists and there are zero copies of the original software it ran on, but shortly after IMAP2 followed, as well as three more revisions of IMAP3, IMAP2bis, and IMAP4 being the current version.


POP, or the Post Office Protocol, was developed with the same intention in mind and has been through several revisions as well, with the latest being POP3, a standard used for a stint on many email services. Developed in 1984, the first iteration was aimed at being a simpler means of accessing emails from a remote server by downloading all messages at once.

POP is the simpler of the two differing protocols, and for the most part has been deemed obsolete given IMAP’s advanced features. POP can access messages from multiple clients, but usually is independent with every device, meaning every email read or deleted has to be redone if re-accessed from another location/device. So, logging in from another device will render many messages as unread, undeleted, flagged, and any organisation of folders will not be replicated anywhere else.

POP3 is advantageous though for servers with minimal storage. The benefit being the fact that the messages are downloaded then deleted from the server upon disconnection, eliminating the issue of duplicate copies consuming space like on IMAP servers.

Also, for those running more deprecated operating systems and/or slower machines may benefit from the low impact of POP3 servers as they consume little memory and CPU.

POP3 listens on port 110 and is a collection of text files for every user which is updated and appended to the bottom of the recipients file once connected. Like IMAP, it will download the newest messages to the computer for local access, but does not continually send updates to the inbox.

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