After clicking All Apps on the start menu does Mail appear under M? You can also type Mail on the search bar, magnifying glass, and the app should appear at the fly-up windows above the search query after the first couple of letters if it is indeed installed but just unpinned. If it does exist in All Apps, the missing tile can be repinned to the Start menu by right-clicking the app and choosing Pin to Start. If Outlook Mail isn't in All Apps, search for it in the Store app. For some reason the mail app is combined with the calendar app as what appears to be one app in the store named Mail and Calendar, but they are two different apps and tiles when installed. An odd change as I don't recall Windows 8 or the phone versions ever installing two separate apps when you think you're installing one. It makes searching for updates and installed apps in a user account a bit more difficult, especially if you have multiple devices and are looking for apps installed on one particular device using the W10 store in your store library. All or nothing.