How to restrict outgoing email to set of addresses

[msp]

Hi

In ISPConfig web interface, Email > Global Filters > Postfix Whitelist, I have added a single email address (type "recipient" restriction). However when I send an email from bash:

echo "this is the body" | mail -s "this is the subject" "to@address"

where the to address is *not* the one I specified in the whitelist, the email is still delivered.

In summary I want to ensure that my server only delivers emails that are addressed to an email address I have specified. (This is for reasons of controlling spam.)

Am I doing something wrong?