You want to know how to add a sender's email address to the Symantec Messaging Gateway block list.

To add an email address to a block list, do the following:

1. Log into the Messaging Gateway Control Center as admin.
2. Click the Reputation tab.
3. Click Local Bad Sender Domains.
4. Click Add.
5. Enter the email address and click Save.
6. Click Save.

For more information, please see the following:

About blocking and allowing messages using sender groups