Add ability to create user account for the user in CC field when email is sent by an authorised user

Problem Definition

When the public signup is disabled and an authorised user sends an email to create issue and at the same time CC a non-existing email address. The ticket will be created but the email address in CC field is ignored without any notification.
Currently JIRA can only create user account for new email address in CC field when public signup is enabled. However some customers do not want to expose the service desk project to every user (when public signup is enabled every user can have access to this project).

Suggested Solution

Add an option in JIRA so that when the public signup is disabled and an authorised user sends an email to create a ticket while CC a non-existing email address, a new user account should be created or a notification should be sent out to notify the sender.
The feature request JSD-988 has been raised to notify the sender in this situation.