Step 1: Log into your Drupal 7 Admin dashboard.
Step 2: On the top menu bar, locate the Configuration option and click on it.
Step 3: This brings you to the main Configuration caterogy screen. Find the subcategory named People and click on the Account Settings link.
Step 4: Once on the Account Settings screen, ensure sure you on the Settings Tab. You can find this in the upper right part of the screen. Under the Emails section, click on the Account Blocke menu option. Click on the Notify User When Account Is Blocked setting to enable it
Step 5: When finished, go down to the bottom of the screen and click the Save Configuration button.