Relying only on inbound sourcing is not going to be enough for your immediate recruitment needs.
This is because inbound sourcing targets only the active job seekers. Whereas many talented engineers who may be interested in your openings aren’t actively looking for a new job.
Sometimes they are occupied with their daily routine, unaware of any new opportunities outside their circle.
Therefore you need to actively reach out to these passive candidates, to tell them of your company and openings. This style of recruiting is called outbound sourcing.