Email Alerts are Not Sent from Sandboxes.
Enable the ability to deliver "All Email." New or Refreshed Sandboxes default to System Email messages only.
Change Access to Send Email to All Email:
1. Log into your Sandbox via test.salesforce.com.
2. Click your Name.
3. Click Setup.
4. Under Administration Setup | Click Email Administration
5. Click Deliverability.
6. Change 'Access to Send Email' from "System Email Only" to "All Email"
7. Verify Email Alerts are sent from your Sandbox.