What is a key feature of the Mail app that enhances user productivity?

The unified inbox for all email accounts is a key feature of the Mail app that significantly enhances user productivity. This feature allows users to manage multiple email accounts from various providers—such as iCloud, Gmail, Yahoo, and others—in a single, consolidated view. By having all emails in one place, users can efficiently track their communications without needing to switch between different accounts or apps. This streamlines the process of responding to messages, organizing tasks, and keeping up with important correspondence, ultimately leading to better time management and increased productivity.

The other options, while useful in their own right, do not provide the same overall enhancement to productivity as the unified inbox. Sending large files easily may simplify the process of sharing documents, but it doesn't centralize communication. Customizing fonts could improve visual appeal in emails, but it doesn’t directly affect the overall efficiency of managing inboxes. Similarly, advanced photo editing tools can be fun and useful, but they don't relate to the core functionality of managing emails effectively.