• Download the Plugin.
  • unzip it and upload wp-restrict-email-domains to wp-content/plugins.
  • Login to Dashboard.
  • Visit Dashboard->Plugins->Installed or Dashboard->NetworkAdmin->Plugins->Installed(If you are using multisite) and activate the “WordPress Restrict Email Domains”.
  • Please Visit Dasboard->Settings->Restrict Email Domains and include the domains/emails/extensions you want to allow.
  • that's it.

Alternatively, you can use the WordPress plugin installer to upload and Install the plugin.