When filtering instant messaging communication on an appliance, one of the methods you can use is to set up a proxy under the XMPP (Extensible Messaging and Presence Protocol).
This protocol is also known under the name of Jabber. It is used, for example, to participate in Facebook chats or Google talk going on between an XMPP client and server.
You can configure settings for the XMPP proxy on the user interface under Configuration | Proxies.
When the SSL Scanner rule set is not enabled on an appliance, traffic going on between an XMPP client and this appliance is not encrypted, but filtered by all rules that are enabled on the appliance. If the client does not accept unencrypted traffic, the connection is closed.
When the SSL Scanner rule set is enabled, traffic is encrypted and inspected using SSL scanning to make it available for filtering by other rules on the appliance.