Is there an option to send a fax to an email address or a Web portal instead of going through Salesforce?
Solution: You can setup automation to email a received fax with the attachment. This requires a VisualForce email template so that it can include the attachment that is related to the Received Fax record. The creation of a new Received Fax record would trigger the automation.
With how the app is built, you can only access the faxes in Salesforce. You could setup a Salesforce Community, Partner portal, customer portal, or force.com license for $25/month for specific users. You could also give these users a login to your Salesforce and setup a limited profile that only gives them access to what they need.