In order to open the mail zip file, I was told, you should KILL and RESTART MobileMail.app. in this way, open mail i could recognize the decompression software.
I used iFunbox save MobileMail to PC, and deleted this folder with iTool from the iPad, restarted my iPad, then the MobileMail folder back to the iPad. But then the Mail could not be opened.
How to reinstall the Mail?