Link Lock is an enhancement to SpamTitan and is available after the purchase of a SpamTitan Plus license. Once a license is in place, an MSP Admin can go to Filtering > Link Lock to enable and configure Link Lock.
This allows a customer or domain admin with "Link Lock Admin" privileges to enable and configure Link Lock for their account. See Link Lock Admin.
Once enabled, Link Lock can be managed at the customer and domain levels. Each level can apply its own Link Lock settings, with settings being inherited from a higher level by default. If applied, a lower level setting supersedes a higher level setting. See SpamTitan Levels of Access.