From the Untangle Wiki: http://wiki.untangle.com/index.php/Quarantine#About_Quarantine
The Untangle Server has the ability to store emails suspected of
containing unwanted content. This repository, a Quarantine, can then
be reviewed to ensure no emails were mistakenly labeled as unwanted
(sometimes called a false positive). The decision to quarantine emails
is made by each Software Product (for example, Spam Blocker). There
are two different types of users that have access to the Quarantine:
End user: Person within the protected network who receives email. End users interact with the Quarantine using a web interface. End
users can purge/release their own emails through a web interface, but
cannot launch the Untangle Server's administrative interface.
Administrator: Person with administrative privileges. The administrator uses the Untangle Server's administrative interface,
Untangle Client, to control quarantined emails for many users.
The Quarantine stores emails that the Untangle Server suspects contain
unwanted content (for example, Spam or phishing). This storage is done
on a per-email address basis. For example, if email@example.com
receives three Spam emails in a day, those three emails are
quarantined for escott. The collection of emails for a given address
resides in an inbox.
If you specify that users receive a Quarantine Daily Digest, the
Untangle Server emails users daily reports that contain a browser link
to the their specific Quarantine inbox. The daily digest emails are
delivered in HTML format, such that they contain links to a web
server. The web server is housed within the Untangle Server. From the
Quarantine, users can manage their quarantined email. End users can
release emails, causing them to be sent to their email clients, or
delete them. In this way, the Quarantine Daily Digest emails enable
end-users to maintain their inboxes.
You may also disable sending of Quarantine emails. If you elect to do
this, users will not have the option to manage their quarantine. If
you receive a huge volume of spam, you may need to modify the Maximum
Holding Time if disk space is an issue for you.
Some users will choose not to act on (ignore) their digest emails. If
a user ignores their inbox for many days (and receives many spams),
their inbox will grow. This is not a concern, as the Untangle Server
automatically deletes emails after a fixed period of time. This time
period is configurable, as discussed in Setting Time Period To
Automatically Delete Quarantined Email.
This option exist for both the "Spam Blocker" and "Spam Blocker Lite" apps, as well as others.