Clients - users of your products who sent an email to the support mailbox or registered a Request through the support site. Clients can be registered manually, or they can register on the support site themselves. A client is created automatically when an email is sent to the support mailbox. In reply they receive an email with a login and password they can use to track the status on the support site.
Companies - group clients into logical groups. These can be employees of one company, or employees of one department if support is provided inside the organization.
Clients are linked to companies automatically based on the domain of the email address from which the Request was sent. For this, the company's Domains field must list the domains (separated by commas). If a client account is created whose email address matches a company domain, that company is linked to the client automatically. You can also edit the client's link to a company manually.
For a company you can set the flag "Employees see each other's Requests". In this case, employees of that company can see Requests that were sent by colleagues. Managers can monitor the Requests that employees sent.
You can control client access to particular support projects or products. If you link support projects to a specific company, employees of that company can add Requests only in those projects. Also, the "Documentation" section shows only the Knowledge bases contained in the linked support projects. This way you can control client access to different documentation sections.
Similarly, if you link companies to products, employees can submit Requests only for those products.