Hi @sinugaud - C8 doesn’t support task listeners the way that C7 did. I think the best approach might be to create a custom exporter that sends the task complete events somewhere to be processed.
Another way would be to create a job worker that listens for the tasks to be created but this is sending the email when the task is created, not completed. Here are some forum discussions about that: Camunda 8 user task, Camunda 8 TaskListener to a user task, and workers for different usertask
I think the BPMN best practice would be that these email events should be part of the model, rather than something that is implicitly done behind the scenes. Explicitly modeling the email tasks makes it clear what is happening and when.