Our testing approach for Marketing Cloud transactional emails will rely on folder organisation and send definition keys that are prefixed with an environment name, as well as different installed packages for each web environment we have (to get around the fact there's no sandbox functionality as with Salesforce Core).
In preparing for this route, we're looking at the Event Notification Service for the Transactional Messaging API and want to have subscriptions for each environment.
I can see from the documentation that it's possible to filter a subscription by the event definition key - would we be able to have a 'contains' condition that filters on the basis that a definition key contains a particular string of text? This would allow us to provide a callback url for each environment we have (via the corresponding installed package) and only subscribe to notifications relevant for that environment.
