The iPhone saves a photo as a set of four when creating an album. Each picture on the set has a specific function (search for file type .ithmb) one of them being the "full photo". This "full photo" is saved on iTunes and it needs to be synced with the iPhone. This app as well as the native Mail app would not be able to send the "full photo" simply because it is not there until is synced. Most likely you will see an error message when opening the Albums which will tell you to sync to get the HD photos (or something very similar).