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Using DomainRestriction is simple. Enter one or more domains into the plugin configs and you're done. Anyone attempting to register an email address that isn't on the approved domain list is immediately denied or vice versa - inclusive or exclusive - it's your choice.
Need more granularity? No problem! Additional configuration allows an administrator to allow specific email addresses in addition to or instead of the domain restrictions! If you want to use it in the opposite manner - you can allow all and deny specific domains and addresses. On special request, I've added the ability to allow/disallow on specific TLDs as well.
At this point, the extension is installed but not enabled. You can find the plugin by going to the Extensions menu and selecting "Plugins". When in the plugin manager, search for "DomainRestriction".
Allow/Disallow based on IP White/Black lists. This is a CIDR capable plugin, so feel free to use CIDR notation to specify networks at your pleasure.
These tabs provide the capability to add individual TLD (Top Level Domains such as COM, NET, ORG), Domains (domain.tld is different than www.domain.tld), and individual email addresses.
Each type is capable of a bulk import which is triggered on paste or if typing, triggered by clicking outside of the textarea. Just select what you are importing and paste (or type). One entry per line.
The plugin has the capability to ignore users who are changing their email, although this may have the opposite effect of the plugin itself. Users could register with an allowed domain, and immediately change to a disallowed domain. Use with caution.
The plugin also has the capability to automatically assign groups based on TLD, Domain or Email - with the added capability of ignoring users who are members of specified groups.
It's fun, try it!
Please report bugs!