Understand domain restriction
The Domain restriction feature lets you restrict access only to the users whose email addresses belong to the verified domain. It secures your application as it prevents users from other domains from gaining access to your application. A verified domain is a domain (eg: xyz.com) that is owned by you or your organization and in which you have all the administrative privileges.
By default, users whose email belongs to any domain can be added to your Zoho Creator application. However, in some cases, you might want to restrict the users with whom the application can be shared based on their email addresses. In such scenarios, the 'Domain Restriction' feature is beneficial.
Domain restriction will be applied to the exiting users of the application. When enabled, the status of the users whose email doesn't belong to verified domain will be changed to 'Inactive' and will not be able to access the application.
For example, let's consider an organization named "Zylker". It has a verified domain "zylker.com" and wants its Zoho Creator application to be accessible by individuals who are part of the organization, but not with those from outside Zylker. To achieve that, Zylker can enable domain restriction in the application for the verified domain "zylker.com". So, the application can be shared with an user with email "email@example.com" but cannot be shared with an user with the email "firstname.lastname@example.org".