Content Settings: LinkLock (Link Protection)

Link Lock: Depicted by the  icon in the editors menu bar. When enabled this feature causes parcel access to lock to the first device and browser from which the link was accessed. By default the Link Lock option is enabled, senders may disable this option on a per-delivery basis by clicking the Link Lock option from the editors menu bar, the icon will turn from  to indicating the Link Lock option has been disabled for the current delivery.

See AlsoModify Content Settings: LinkLock