Recently I was asked to create a plugin which allows new user to register with specific list of email-domains. For e.g. i want to allow to register only those users who have gmail addresses.
I was not aware of whether the site is using Jomsocial.
So created two plugins one user plugin for Joomla registration & community plugin for Jomsoical.
Added snippet for jomsocial on onRegisterValidate event & for joomla its onBeforeStoreUser.
Compared entered email domain with the list of email-domains configuration parameter of the plugin.
I was thinking of creating just a plugin instead of two plugin but didn't get jomsocial data on joomla's onBeforeStoreUser event. That's why created two plugin.
You can download these plugins here for Jomsocial & Joomla