Guard Rails is now available in open beta for Courier, allowing businesses to set upper limits on message sending per time period. This feature provides various time periods such as billing period, hour, day, week, and month, with notifications sent when a limit is exceeded. Tenant admins receive a notification email if throttling occurs, ensuring critical messages are prioritized. Additionally, email open tracking is now supported even with template overrides, allowing for easy tracking of opened emails in Courier logs. Various improvements and fixes have also been implemented to enhance the overall user experience.