If a switch receives a frame whose destination MAC is not in its MAC address table, how does it handle the frame?

When a switch receives a frame with an unknown destination MAC address, it floods the frame out of all interfaces except the one it was received on. This is a broadcast-like behavior at Layer 2, designed to ensure the frame reaches its intended recipient if it exists on the local network segment. If the destination host replies, the switch will then learn its MAC address and update its MAC address table for future communication. Sending an ARP request is a Layer 3 function performed by hosts to resolve IP addresses to MAC addresses, not a switch's action for an unknown MAC. Updating the destination MAC to FFFF.FFFF.FFFF would turn it into a broadcast, which isn't the default behavior for an unknown unicast. Dropping the frame would prevent communication and is not the initial action for an unknown unicast MAC address.