What key feature distinguishes IMAP from POP3?

The key feature that distinguishes IMAP (Internet Message Access Protocol) from POP3 (Post Office Protocol version 3) is that IMAP generally leaves email on the mail server.

With IMAP, users can access and manage their emails directly on the server, which means that messages can be viewed and organized across multiple devices without being downloaded and removed from the server. This is particularly beneficial for users who access their email from different locations or devices, as all interactions with the email—such as reading, deleting, and organizing—are synchronized with the server. Thus, the emails remain available on the server, ensuring that users have access to the same set of emails regardless of the device they use.

In contrast, POP3 typically downloads emails to the client device and deletes them from the server (unless configured to leave a copy), which can lead to issues if users want to access their email from multiple devices. This fundamental difference in how emails are stored and accessed is what sets IMAP apart from POP3, making option B the correct choice.