Since I updated my iPad 2 to iOS 8.3 I noticed that under 'Usage' the 'Mail' level was very high (4.5GB) when on my iPhone (which I have not updated) it was only 850MB. Even after deleting all my email accounts on the iPad the usage still remains at 4.5GB. I have tried soft and hard reset but the issue remains. Help please!!
Backup your iPad (iCloud or iTunes), and restore it using iTunes: https://support.apple.com/en-us/HT201252 This should remove most of the usage for Mail. You'll be able to restore from a backup afterwards.