Postfix blocking domains

How to block sender domains

sudo vim /etc/postfix/sender_access

Add lines like this:
email@domain.com REJECT
domain.com REJECT

Then run:
sudo postmap /etc/postfix/sender_access

Then add or edit the following in main.cf:
sudo vim /etc/postfix/main.cf

smtpd_recipient_restrictions = check_sender_access hash:/etc/postfix/sender_access

Save and exit. Then run:
sudo postfix reload