I'm midway through Eric Evans' DDD book but don't think this question would be answered in the book.
If an application has its own complicated concepts different from the underlying domain, can we create another domain model for representing the application too?
An example would make it clear. Say, the core domain of an organization is Information Rights Management, that is encryption of information and control of its usage according to access rights of users. One of their applications is an IRM enabled e-mail client like Outlook which encrypts outgoing e-mails using IRM. Now, an IRM enabled e-mail client is in itself a very complicated application and may have several new business rules regarding IRM in e-mail, entities, and operations. In such cases, is it wise to make another domain model to represent an E-Mail client only within the application and use both the core IRM domain model and the e-mail domain model together? Note that IRM in e-mail is not the core business of the organization but nonetheless they have an e-mail client that revolves around IRM.