Explain the differences between POP and IMAP4.

POP
· The Post Office Protocol, version 3, is a standard protocol with STD number 53.
· Its status is elective, and it is described in RFC 1939.
· The older Post Office Protocol version 2, defined in RFC 0937, is a historic protocol with a status of not recommended.
· The Post Office Protocol is an electronic mail protocol with both client (sender/receiver) and server (storage) functions.
· POP3 supports basic functions (download and delete) for electronic mail retrieval.
· More advanced functions are supported by IMAP4 .
· Using POP, a client must always be connected to the server for changes to be made.

IMAP4
· The Internet Message Access Protocol, Version 4 is an electronic messaging protocol with both client and server functions.
· It is defined by RFC 3501.
· Similar to POP, IMAP4 servers store messages for multiple users to be retrieved upon client requests, but the IMAP4 model provides more functionality to users than does the POP model.
· IMAP4 allows clients to have multiple remote mailboxes from which messages can be retrieved, and allows users to choose any of those at any point.
· IMAP4 clients can also specify criteria for downloading messages, such as not transferring large messages over slow links.
· Additionally, IMAP4 always keeps messages on the server and replicates copies to the clients. · However, IMAP4 allows clients to make changes both when connected and when disconnected.
When disconnected, (referred to as a disconnected client), changes made on the client take effect on the server by periodic re-synchronization of the client and server.