We have connected above clouds using v5 Marketing Cloud Connector, and everything is working fine, when er are using the Account ID as Subscriber Key. We can both send emails, and tracking is successfully sent back to Salesforce.
We are working in an enterprise landscape, where we need a common ID across all systems, and until now, we have been using Contact ID for this. However we are looking into switching into using a custom ID instead. If we are to keep using Marketing Cloud for sending out transactional emails, this ID should also be used as Subscriber Key, qua the need for including this in API calls triggering transactional email.
However, when testing using this custom ID as Subscriber Key, we are not able to receive tracking back into Salesforce, on individual level. Only aggregated email results are available. Is there a way of changing which ID should be used as subscriber key?