Modules

Where are Drupal8 contact forms entries stored?

Contact form

Contact Storage module will provide storage for Contact messages which are fully-fledged entities in Drupal 8.

This plus core contact module aim to provide functionality equivalent to the base-features of Webform or Entity Form.

Contact Storage

https://www.drupal.org/project/contact_storage

Contact Storage module provides storage for all the messages submitted through the forms on your site as well as views integration to manage them.