Which mail retrieval protocol is designed for mailbox management and operates over port 143?

The protocol designed for mailbox management and operating over port 143 is the Internet Message Access Protocol (IMAP). IMAP allows users to access and manage their email on a remote mail server. One of the core advantages of IMAP is its capability to maintain the state of the mailbox across multiple devices, which means that when an email is read, deleted, or moved into folders, those changes are reflected across all devices accessing the same mailbox. This functionality supports more complex activities, such as searching for messages, flagging, or creating folders on the server.

In contrast, Post Office Protocol 3 (POP3), typically operating over port 110, is primarily designed for downloading emails from a server to a local device, which often results in emails being removed from the server, limiting multi-device access. Simple Mail Transfer Protocol (SMTP), utilized over port 25, is not intended for retrieving emails but rather for sending them. File Transfer Protocol Secure (FTPS) is unrelated to email retrieval and is designed for secure file transfer over a network. Therefore, IMAP's features and its designated port of 143 clearly define it as the correct choice in this scenario.