Outlook Express 7 introduced various changes to the user interface[4] and relied on WinFS for the management and storage of contacts, email, and other data.

[8] Windows Mail was formally announced on September 16, 2005 at Channel 9 and positioned as the successor to Outlook Express.

The storage of items is managed by a Extensible Storage Engine database — the same engine used by Active Directory and Microsoft Exchange — with messages and newsgroups stored as separate eml and nws files instead of in a single dbx file; the database is transactional and periodically creates backups of items to protect against data loss, which eliminates the single point of failure design of Outlook Express.

[11] Windows Mail has a documented application programming interface (API) based on Component Object Model (COM).

[citation needed] Mail in Windows 8 and 8.1 is a completely new application based on the Windows Runtime, designed in accordance with Microsoft's Metro design language philosophy, as a Windows Store app that runs in either full-screen or split-screen viewing modes; many of its features are hidden in the charms or in the app bar (an initially hidden toolbar) at the bottom of the screen that is revealed by right-clicking or by swiping upward.

Mail is updated independently from the operating system and is bundled with Calendar and People—it cannot be installed or uninstalled individually.

Users can set Mail to use the system theme or choose a custom accent color, background image, and light/dark preference.

[22] In December 2019, Mail added non-removable advertisements for the Microsoft Outlook mobile app.