Which email app are you using? It could be in a variety of places but the best way to find it would be to just open up the gallery if it's a photo or an office app if it's a document. If it's a zip or something else like that, it could be in /sdcard-ext/download, or another location created by the app. Sometime apps create folders all over your internal storage and SD card and it can be really annoying to find where they saved something to.
It probably downloaded it to your SD card somewhere then, so if you open an office app it should automatically find it just like your gallery finds all your photos