The changes are largely in keeping with those seen elsewhere as part of Microsoft's Office-wide overhaul. There's bolder typography (although the fonts remain native to the iPhone and iPad) and more vibrant colors, designed to help users identify and quickly switch to Outlook among a sea of monochromatic apps. Headers and message lists shrink and expand dynamically as you scroll, and the animated calendar icon fans forwards and backwards as you scroll through your agenda.

Microsoft has also introduced new sensory feedback to create what it calls a "resonant experience." You'll see subtle changes in color, shape and iconography when you swipe left or right on an email, and of course there's plenty of haptic feedback to reassure you that stuff is happening (this can be switched off).

You'll also see some changes that make the business of using the app more efficient, too -- not just prettier. Potential meeting conflicts are instantly identified, and events can be scheduled without typing a single letter: the update brings forward all people, dates and place elements required into context so you can simply slide options around the calendar to find a time and place that works, no typing required. And if you have multiple accounts and calendars in the app, new account icon cues will help you easily switch between them.

An interface upgrade has been a long time coming for Office, and Microsoft has clearly put a lot of effort into getting it right -- not just on mobile but across the board. The updated icons in particular reflect the company's changing direction, away from an almost exclusive focus on Windows and into the cloud, where -- as illustrated by this refresh -- design takes on an importance that Office has never seen before.