Choose your Platform: full shortcut list + printable PDF
Windows Ctrl as the modifier in the new Outlook for Windows. Single-key ribbon key tips (press Alt, then a letter) reach any command that has no direct shortcut.
Web Ctrl as the modifier, and most mail actions also answer to a single bare letter (N, R, E) with nothing held down, a lighter shortcut set than the Windows desktop app.
Mac Command as the primary modifier, with Option and Control covering search, formatting, and pane navigation.
iPad Command chords with an external keyboard, a smaller set focused on composing, replying, and moving through the message list.