The External Sharing feature enables your users to share a specific form with external users (those with no access to your SharePoint environment). These external users will be able view and edit the form and participate in any workflow you have defined. When this feature is enabled external users can receive an invitation email containing a link to the form and clicking on the link will open a page where they can request a temporary pin. The system will email them the pin and once they enter it they can open the form.
To enable External Submissions navigate to the Sintel Forms Designer -> Settings -> External Submissions
The External Sharing can be used without requiring the External Submissions or the External Collaboration features to be enabled.
You can also customise the invitation email that is sent to users when sharing a specific form with them.
External Sharing is ideal for ideal for scenarios where you need to involve external people in populating data in your forms without giving them any access to your Office 365 / SharePoint Online environment. Things like gathering feedback and collecting signatures are now super easy to accomplish.