Which protocol uses port 143 and is designed to sync email across multiple devices?

The protocol that uses port 143 and is designed to sync email across multiple devices is IMAP, which stands for Internet Message Access Protocol. IMAP allows users to access and manage their email from different devices while keeping the email stored on the server. This means that actions such as reading, deleting, or moving messages are reflected across all devices that access the email account.

IMAP is particularly useful for users who check their email from multiple locations or devices, such as smartphones, tablets, and computers. It maintains the state of the messages, enabling users to see which emails have been read or folders that have been organized without altering the data stored on the mail server.

In contrast, other protocols mentioned do not serve the same function. For example, LDAP (Lightweight Directory Access Protocol) operates on different ports primarily for directory services rather than email. SMTP (Simple Mail Transfer Protocol) is used for sending emails and typically operates over port 25 but does not manage emails across multiple devices. DNS (Domain Name System) is responsible for resolving domain names to IP addresses and is not related to email synchronization. Thus, IMAP is the appropriate choice for the given context of synchronizing email across devices.