Which command will drop a matching packet and send out a notification message?

The `no-retain` option prevents a static route from being retained in the routing table if its next-hop interface becomes unavailable, but it does not drop packets or send notifications.

The `discard` keyword causes packets to be dropped silently without sending any notification message, which is contrary to the requirement of sending a notification.

The `reject` keyword configured as the next-hop for a static route explicitly instructs the Junos device to drop any packet matching that route and concurrently send an ICMP Destination Unreachable message to the packet's source, thereby providing a notification.

The `no-install` option prevents a static route from being installed into the forwarding table, meaning it won't be used for actual packet forwarding, but it doesn't actively drop packets or send notifications.