With Web Services now configured for secure connections, the final step in the configuration is to amend the Workflow setup. This is done via the Workflow Setup window (); despite this being on the System part of the menu, it is actually a Company window so any changes made will need to be repeated in all companies using Workflow.
There are two settings which need to be changed; both of them in the Enable E-Mail Actions section.
Change the Server Name to the externally accessible DNS hostname, change the Port to the relevant port and mark the This server requires a secure connection (SSL):
Once you’ve changed the settings, click the Test E-Mail Action button on the action pane. A confirmation dialog will be displayed: