cd /etc/postfix
# nano sender_access

Append sender email id as follows:
user@abadboy.com REJECT

Save and close the file. Use postmap command to create a database:
# postmap hash:sender_access

Now open main.cf and add code as follows:
smtpd_recipient_restrictions = check_sender_access hash:/etc/postfix/sender_access

Save and close the file. Restart / reload postfix MTA:
# /etc/init.d/postfix restart