You can define a list of comma-separated email domains such that the system allows sending emails to only those domains. Outgoing emails to any other domain i.e. other than those listed will be prohibited.

Procedure:

  1. Go to Configuration → Email Gateway → Enable Outgoing Domain Whitelisting.
  2. Provide a list of email domains to be white-listed. Separate them with commas.
  3. Click on Save.