Thoughts that are my own.

Blocking Individual Email Addresses Using Postfix

Change to the Postfix configuration directory. Usually this is in /etc/postfix.

cd /etc/postfix

Open the sender_access file or create it if it doesn’t exist.

vi sender_access

Add the email address you want rejected on a new line in the file followed by REJECT. REJECT

Save the file.

Create the server_access database with the postmap command

postmap hash:sender_access

Edit the file and add the following

smtpd_recipient_restrictions = check_sender_access hash:/etc/postfix/sender_access

Restart Postfix

service postfix restart

Check your logs to make sure everything is good.