Allow email domain restrictions for public signup

Problem Definition

In certain cases, Service Desks need to be restricted to a set of customers belonging to one and the same organisation.
Public signup does not provide a proper means to prevent incorrect customer accounts not belonging to that organisation from being created.

The only alternative available right now, is to disable public signup, which has as a result that the Service Desk administrator can get presented with significant amounts of work solely for account creation.

Suggested Solution

As such, being able to define an email domain as requirement for public signup, can provide a small degree of safety, while at the same time prevent a lot of overhead for the administrators.

For instance, if a Service Desk has public signup enabled, and an email domain has been defined, the Service Desk will only allow account creation if the source address conforms to the defined domain.