Had the same problem and did some tests. For me the battery drain was caused mostly by different apps running in the background and updating via my wireless connection (not WiFi). The emails are actually a large part of this and it is difficult to switch this off (have changed the settings for updating my mail).
Did other things too (screen brightness, closing apps, etc.) but the mobile data was the worst by far.
Finally, if your phone is old (over 2 years) you may consider changing the battery and/or doing a restore to factory settings to remove clutter.