The CSV export option is available with a Growth, Pro or Business plan only.
There is a limit of 5000 emails per domain that can be exported in the Domain Search.
The Domain Search results are limited to 10 email addresses in the Free plan.
With a Starter plan you have full access to the Domain Search results (based on the Search requests left in your plan).
Is there a limit in the Bulk Domain Search?
When using the Bulk Domain Search, at most 100 emails can be extracted per domain. This is to encourage our users to build more qualified lists rather than big and low-quality exports. Each Bulk Domain Search is also limited to 25,000 domain names (or company names ) maximum.