For each supplier, you can define periods of unavailability. When outsourcing a job, the system indicates if a supplier is available at that moment. Your search for the right supplier for a job is then optimized.
To define a period of unavailability for a supplier, you have to click on the Availability tab in the supplier's details under People > Suppliers (on the left).
You can then easily define a period of unavailability by clicking on the "Add unavailability" button.
This is what it looks like when you add entries:
You can of course delete any of these entries or modify them using the buttons on the right.
In the Outsourcing tab of the job, the system then indicates if the supplier is available at that moment and until when he/she is available: