Post Office Protocol (POP) is another protocol for retrieving email messages from a mail server. It is similar to IMAP, but it has some key differences.
One difference is that POP is typically used to download email messages from the server to the client device, rather than accessing them on the server. When a client retrieves email messages using POP, the messages are transferred from the server to the client, and are usually removed from the server. This means that the email messages are not available on the server after they have been downloaded to the client.
Another difference is that POP does not provide as many features for accessing and managing email messages as IMAP does. For example, POP does not allow the client to search for specific messages on the server, or to download only the headers of messages.
POP is often used with email programs that run on a single device, such as a desktop computer or a smartphone. It can also be used with web-based email services, but it is less common than IMAP for this purpose.