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How to encrypt your Postbox (or other) email on OS X

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April 21, 2011

Postbox stores your IMAP archives in plain text

Postbox stores your IMAP archives in plain text

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Even if you're using IMAP to access your email, certain newer email clients like Thunderbird 3 and Postbox will download and store your emails locally in plain text. This leaves many users making a difficult choice between leaving sensitive data unencrypted, or venturing into overkill territory by using a tool like FileVault, PGP Whole Disk Encryption or TrueCrypt - which see you encrypting your entire home directory or hard drive and dealing with a performance overhead. This article will show you how to encrypt only your Postbox email on a Mac, but can easily be adapted to other email clients (or other folders like your Documents folder).

Before we get started, be aware that this method utilizes an encrypted sparse bundle, which is only available in Leopard and Snow Leopard.

1. Close down your email client

2. Open Disk Utility from the Utilities folder (/Applications/Utilities)

3. From the File menu, select New > Blank Disk Image (option + command + N)

4. Use the following settings (the size can be whatever you'd like, but sparse bundles only consume the space they need to, so I suggest using a generous size to avoid potential headaches later)

Creating your encrypted sparse bundle

5. Save the disk image as postbox.sparsebundle in the root directory (which is most likely "Macintosh HD")

6. Enter a password that you won't forget, and add it to your keychain (bearing in mind that the disk image won't be secure if you don't have a login password set on your machine)

7. Open a Finder window and navigate to your home directory (shift + command + H is a handy shortcut)

8. Go to Library/Application Support/

9. Rename the Postbox directory (or the Thunderbird directory, or...) to "Postbox Old"

10. Copy the contents of the Postbox Old directory (not the directory itself) to your new disk image, which can be accessed via the icon on the desktop or the devices pane in the sidebar of a Finder window

11. Open Terminal

12. Type "cd Library/App", press tab and then press enter

13. Type "ln -s /Volumes/Postbox/ Postbox" and press enter (if you named your disk image something other than Postbox, you'll need to substitute /Volumes/Postbox/ for whatever name you used)

Creating a symbolic link to your encrypted email

14. Open the System Preferences from the Apple menu

15. Go to Accounts

16. Go to the Login Items tab

17. Press the + button

18. Add postbox.sparsebundle from your root directory, and then tick the Hide box

Mount your encrypted email on login

19. Open Postbox. If everything went well, Postbox should be running exactly as it was before we started, except your email archives are safely encrypted. For additional security, you may want to set your login keychain to lock after a certain period of inactivity, or when your computer goes to sleep - you can do this using Keychain Access in your Utilities folder.

20. Now that we've verified everything worked, you can go and delete the Postbox Old folder we left behind in step 9.

Any issues? Let us know in the comments.

About the Author
Tim Hanlon Tim originally came to Gizmag as a developer, much to the dismay of anyone who had to maintain, build on, or rewrite his code. After wearing every other hat that didn't have a head for it, he became CEO in 2010. He's a racing sim tragic, an amateur martial artist, a nacho enthusiast, and a (mostly) reformed electronic musician.   All articles by Tim Hanlon
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4 Comments

Macs are for kids, why on earth would kids need to worry about Encryption?

Michael Mantion
21st April, 2011 @ 08:25 am PDT

PCs are for kids... Go back to your World of Warcraft, Michael! :)

Chevypower
21st April, 2011 @ 11:08 am PDT

Macs and Linux are both the way to go. GO UNIX!!!

Red Bike Master
21st April, 2011 @ 01:12 pm PDT

Thank you for that. It addresses exactly a need that I have been trying to resolve for some time. Nicely done. (Now I'll go & try it :? )

Sqidge
22nd April, 2011 @ 05:08 am PDT
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