Visit the official WordPress repository page to install or download the plugin.

Download plugin

Free WordPress Plugin

One Time Email Access Guard

Search One Time Email Access Guard from the Plugins page and install it.
Otherwise manually upload the one-time-email-access-guard folder to /wp-content/plugins/
Activate the plugin from the Plugins menu
Go to Access Guard in your Admin menu
Create users with their contact details
Enable protection on any page/post and assign authorized users

If you use this plugin and want to support its development: support the project

"One Time Email Access Guard" is open source software. Contributor: Marco Gargano