Is there a way to do this?
YES my friend there is away, i do it by myself and it's work well…
Here are the steps:
1. go to "/Applications/Mail " and "get info" for your mail and look how much is size of it.
2. from "/Applications/Utilities" open "Disk Utility"app.
3. from file menu select "Blank Disk Image".
4. Save as: "chose the name you want" I save it as "Mail".
Where: "Better to be on Applications Folder" or in Privet Place on your hard.
Name: "chose the name you want" I name it as "Mail".
Size: set the size Bigger than the size of Mail you take it from "mail info".
Format: Mac OS Extended (Journaled).
Encryption: 128-bit AES encryption.
Partitions: Hard disk.
Image Format: sparse disk image.
5. when you finish Press "Create".
6. Enter the Password You need, be sure to remove the mark next to "Remember password in my keychain".
7. press "OK".
8. you will find new hard disk open on desktop called "the name you chose it before".
9. now copy "Mail.app" to the new hard disk, and remove mail.app to trash but don't empty it. "if you can't delete the app get the info of it and make all the Permissions Names Read & Write" you need Administrator password to open the lock down below.
10. now remove the mail shortcut in Dock and drag the Mail.app you copy it to Dock.
11. now Eject the new Hard disk.
12. open mail from the Shortcut you add… it's will ask you for a Password.
Be sure to Eject the hard disk when you finish from mail.
DONE