Like the mobile versions of Outlook, the Mail & Calendar app learns which emails you're likely to either read or reply to and filters the important ones into the Focused Inbox. Everything else gets filed away in the the easy-to-neglect "Other" tab. The filters can also be tweaked by manually flagging a message for one inbox or the other.
As for the mention system, users can now tag each other in an email by typing the @ symbol to bring up a list of contacts, similar to how the web version of Outlook currently works. Selecting a contact adds that person to the chain and will highlight their name in the body text so they can see exactly where in the chain they've been mentioned. Users can also filter their emails to search for ones where they've specifically been tagged.
On the calendar side, the app is also getting intelligent travel reservations and packaged delivery reminders based on your emails, as well as some new color categories and the ability to subscribe to popular calendars like holidays and sports schedules.
Microsoft says the new features are currently rolling out to Mail & Calendar users with Office 365 and Outlook accounts over the next few weeks, and that they'll be bringing the same features to third-party email accounts in the near future.