Mail Rate Limiting not working

in Email Settings -> Mail Rate Limiting I have the following settings:
Rate limiting enabled? yes
Global message limit 5 emails every 1 Hour (just to test that it does not work)

When I now send 20 emails via PHPmailer, they get queued in the postfix server and sent out immediately.
Am I interpreting the “Mail Rate Limiting” wrong? I want to limit the emails sent out by my server to not get caught in spam filters.


Mail Rate Limiting

This page allows you to control the rate at which your system’s mail server will accept new messages. By default any script on the system or remote sender with an SMTP login can send email with no rate limits, which can be a problem if a login or script is hijacked by a spammer. This feature lets you set a reasonable limit, such as 1000 messages per hour across the whole system.

In addition to a global limit, you can also set per-sender domain rates. These will override any global limit, and can be used to grant a particular trusted domain a higher or lower limit than what applies to others.