What happens if a letter doesn't reach the destination addressed on the envelope and doesn't have a return address?
it gets binned
What happens when the switch receives a frame addressed to a new host that is not yet in the mac address table?
It will slow the delivery, as the envelope may need to be processed by hand. The sorting machines will orient the envelope so that the stamp is in the upper right corner. It will cancel the stamp and try to read the address. Since the orientation is wrong, it will probably fail and be kicked out for hand processing.