Normally when you enable encryption, an outbound rule should be created automatically for your oganisation that will trigger encryption of 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
Also we recommend creating a filter rule if in outlook, you mark the email as confidential.
When you compose an Email in outlook, you can click the "Tags" option and set Sensitivity to "confidential".
The corresponding filter rule would look like this:
If Email Headers CONTAINS ANY OF company-confidential DO encrypt