TestFlight sends automatic e-mail notifications to beta testers, with the subject "AppName 1.2.3 (123) for iOS is now available to test." etc.
At the bottom of these messages is an "Unsubscribe" link, which is a mailto: link that sends an e-mail to the app's support contact address with of the form
mailto:developer?subject=Unsubscribe from TestFlight&body=tester wants to stop receiving TestFlight emails about AppName
Unfortunately, app developers cannot manage an individual testers' notification settings. This creates a frustrating support loop where the developer has to reply directing the tester to disable e-mail notifications for themselves within the TestFlight app.
Am I missing something? (Also reported to Apple as FB19806347)