Support Ticketing module - clients
Think of "Support Client" as entity that pays for support. Or would pay if you'd charge. On your site you probably want two support clients: your company and external. Or, if you are B2B company, each of your client business should be defined as a support client, plus one for your own company. Then you can tie roles with support clients, like "marketing department" and "sales manager" are roles that belongs to "internal" support client, and "example company representative" belongs to "example support" support client.

Benefit of this is: all your internal roles can participate in your internal issues, and all roles of one of your clients can participate in theirs, but clients cannot peek at each other's support tickets, or at your internal ones.