Jun 4, 10:08 PM
How to run Apple Mail from an External Drive or Encrypted Volume
Here is how to move Apple’s Mail.app to an external drive or encrypted volume. This has been tested on Mavericks. Make backups before you attempt this in case something goes wrong.
Overview
You will need to move your mail folder to the drive, create a symbolic link to it, replace the original folder with the symbolic link, and enable spotlight indexing of that drive.
How to Do It
First quit Mail.app.
Download and install the Symbolic Link Maker service. This will add a context menu entry to create a symbolic link. You may need to restart/logout/login to complete installation.
Then make sure the volume/drive you’re moving the mail folder to is formatted as Mac OS Extended (Journaled). Let’s assume its volume name is MAILDRIVE, but you can name it anything.
Now copy your /Users/[username]]/Library/Mail folder to MAILDRIVE.
Then back in the original location, drag the mail folder out onto the desktop for now.
With the Mail folder copied over to the target drive/volume, right click (or CMD click) on the Mail folder, go down to “Services”, choose “make symbolic link.” It will create a symbolic link called “Mail symlink.”
Drag that symlink to the original mail folder location, and rename it simply “Mail”
So now the original folder has been moved and a redirect (symlink) put in its place that points to its new location.
Next, open up Terminal and enter: sudo mdutil -i on /Volumes/MAILDRIVE … enter your password when it asks. Then it should say after a few seconds that indexing has been enabled on MAILDRIVE. This will enable Spotlight indexing. Otherwise you won’t be able to search your mail messages.
So now you can open up Mail, and after Spotlight indexes the drive/volume you’ll be able to search messages and operate as before.
Notes
Yes, if your Mail folder is on an encrypted DMG or Truecrypt volume, Spotlight is a security risk. Weigh that before doing this. For example, it would be good enough to keep roommates and thievess from accessing your mail, but not some professional who combs through the Spotlight index and tries to piece together the contents of your emails.