Last night we put our own CNAMEd domain into the "Portal URL" admin box.
Previously, ticket links sent to customers (http://ourcompany.freshdesk.com/helpdesk/tickets/3889) went straight to the ticket. The new links (http://ourdomainname.com/helpdesk/tickets/3919) go to the login page rather than to the ticket. Our "Who can view tickets on portal" setting is on "Anyone with public ticket URL" but that doesn't seem to be the case.
The impression I got from support was that this is expected, and that there's no way to view a ticket without logging in first unless you're using the freshdesk.com domain.
Is that correct?