Workflow Rule and Process Builder: Email Alert Does Not Utilize Bounce Management Address

This behavior is standard functionality and working as designed.  

If an Organization has a Workflow Rule or Process Builder configured to send out an Email Alert on the Contact or Lead object, the process will not utilize the Bounce Management feature (enabled under Setup | Email | Deliverability). Bounce management works with mails sent directly from the Contact and Lead record by a user.  However, if the receiving email address is invalid, the sending address will receive a Mailer-Daemon bounce from Salesforce.com (if these emails are not blocked by the receiving mail system). 

This behaviour only applies when reply Email address in My Email Settings is salesforce.com domain. If we change the Email address to gmail.com domain, IsEmailBounced is set as True in the same scenario. 

For Further Information see: Bounce management fails occasionally for none Marketing Cloud emails