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.
Apple release new updates from time to time for all OS X… Some times the Mail.app give an Error Message… here is the steps for how to Fix this Error for all versions of Mac OS X…
1. before you update to the new Update of OS X you already had "10.5.__ - 10.6.__ - 10.7.__ - 10.8.__" - Copy the Mail.app from "sparseimage" disk you great it before from where you save it to "/Applications" Folder.
2. Now update.
3. after you update and restart go and Open Mail.app from "/Applications/Mail.app" the app will open Normally.
4. Now copy the Mail.app to the "sparseimage" Disk and Replace the old Mail with the new.
5. Delete the Mail.app from "/Applications" Folder.
6. open the app and it will work Fine.
Note: if you update before you do this Steps.. Don't worry you can do the same steps and update the System again.. and the Mail.app will work Normally.
Best not follow these steps. It will work until the next Mail update. But it makes no sense to want to protect mail this way and leave other areas open....So you go and password protect the Mail app. Ok so I can't open Mail but I could easily go to your Mail folder in your Library folder and copy all you mboxs and emails to a USB stick for later viewing. You would do best to protect your account using a combination of a firmware passowrd and login password. Keep it simple