End-user ticket view links in email notifications return 404 or ask for username/password instead of showing the ticket thread anonymously.

Ensure the following setting is enabled: Admin Panel > Settings > Tickets > 'Enable HTML Ticket Emails' / 'Enable Auth Token' (the setting that allows unauthenticated access via a token link). Also verify that the URL base in templates uses the correct domain (not /osTicket/ subdirectory if the site is at the root). If links intermittently fail, this is a known Guest User session issue -- clearing browser cookies/cache resolves it temporarily.