Configure Allowed Email Patterns

Hi, I am trying to follow this guide: 4.5. Specifying Allowed Registration Email Patterns — Installing, Configuring, and Running the Open edX Platform documentation. I added the following to config.yml:

REGISTRATION_EMAIL_PATTERNS_ALLOWED: [
   "^.*@(.*\\.)?mydomain\\.dk$"
]

However it does not have any effect. Is there any other specific place I should use instead for this parameter? Thanks a lot in advance.

I found out that it must be done via plugins.