If the recipient is receiving an email after a task is being finalized, it means that the default email recipient is enabled on the device. To deactivate the automation, you can go to your licence > menu > settings > additional preference. There, you can uncheck the box “Add default email recipient”.
On the other hand, if the box is checked, but the task does not have any contact emails, then certainly, the system will not send any emails. Therefore, it is wise to check the settings beforehand.