In this section, you can define a folder into which infected files may be moved automatically when they're found.
To do so, click the "Set Quarantine Folder…" button and navigate to a folder on your hard drive where you want to put the infected files. If you don't have a preference for where to put them, after pressing the "Set Quarantine" button, press cmd-shift-H on your keyboard to get to your Home folder and then click the "New Folder" button on the bottom left. Call the new folder "Quarantine", click "Create", then click "Open".
Once a folder has been set, you will see it listed beneath the checkbox. It cannot be unset, however, it can of course be changed.
You can then enable and disable the auto-quarantine option by clicking the checkbox to the left of the button.
Please be careful with this option - if a message in your email mailbox is infected, this option has the potential to move your entire mailbox (with the exception of Apple Mail) away from where it should be, rendering your email missing and inoperable! In most cases, it can be moved back to where it should be, but on the whole it's not an easy task. If you find yourself in this situation, do not quit ClamXav, rather you should immediately select the item in ClamXav's Infection List and select the File menu » Infection list » Put Back.