The following filter has to be configured to enable the encryption functionality of the Vircom plug-in.
Normally when you enable encryption, an outbound rule should be created automatically for your organization that will trigger encryption when you click "send secure" assuming you have the encryption plug-in installed. It can happen from time to time that this rule does not get created (for instance, if you switched from "Business" to "Advanced" and back to "Business" at some point). You can manually create the rule like this:
The filter rule should look like this:
if Email Headers CONTAINS ANY OF x-proofpointencryptdesktop DO encrypt