This is not ideal for example where club members are children and they should be registered with a parents address. It also makes creating test users more difficult as they all need to have separate addresses.
Duplicate Email Plugin for Joomla
This system plugin allows administrators of Joomla sites to enable users to register more than one account with the same email address. It works by overriding a core class to disable the duplicate email check.
The plugin also uses the Joomla Update feature to check for new versions and enable simple updates when new Joomla versions are released
This plugin is based on the users same email plugin - (C) www.iss-profesionalia.com. If you are using that plugin then it must be removed before installing this plugin as they both try to override the same core class.
We are always open for your suggestions and complaints, Please reach us.