[Megatr0n]

Add these features:

* The system can be turned on and off globally.
* Configurable invite expiration period.
* History of issued invites, with color highlights and options to purge pending, expired or rejected invites.
* Daily invite reminders and expiration notifications, can be turned off if desired.
* Ability to define how often reminders can be sent.
* Ability to reject received invitations.
* Ability to permanently opt out of receiving future invitations, with automatic marking of invite as rejected and with an admincp database management interface.
* Automatic prevention of invites from being sent out to already registered e-mails.
* Automatic prevention of invites from being sent out to the same e-mail multiple times.
* It is possible to either keep registration process open or to restrict it to invited registrants only.
* Ability to define users as "First Friends". Such users become mutual buddies with all new registrants, whether invited or not.
* If registration is open, the number of invites each member owns is unlimited.
* If registration is private, invites are allocated automatically at the end of each week based on activity. That can be turned off from admincp.
* If registration is private, expired and rejected invitations return invite credit to the issuer's account.
* As an alternative to automatic allocation (which can be turned off), there is an "Allocate Invites" tool, which gives you an ability to give out X invites to members that match a certain criteria.
* Amount of invites owned by a user is directly editable via admincp user management interface.
* In addition, a configurable number of invites is given out on reputation change.
* If applicable based on user's permissions, an "Issue New Invite" prompt is displayed in usercp for that user.
* When an invitee signs up, invite issuer is automatically set as a referrer for the invitee, and there is no way to go around that.
* When an invitee signs up, invite issuer and the invitee are automatically set up as buddies. Can be turned off from vBulletin Options -> Invites System
* When an invitee signs up, the invitee can be automatically put directly into a special usergroup, if such specified in the issuer's usergroup settings.
* Human verification to prevent multiple submissions.
* Usergroups can be either allowed or disallowed to issue new invites.
* Members can be configured to either go along with or override the member's usergroup setting.
* Inactive users gradually lose their invites. How many invites are lost for each week of inactivity is up to you - the number is configurable from vBulletin Options -> Invites System.

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Taken from: http://www.visionscripts.com/?page=products&productid=3