d Abstract) Marcos K. Aguilera1 , Eli Gafni1,2 , and Leslie Lamport1 1 Microsoft Research Silicon Valley 2 UCLA We propose and solve a synchronization problem called the mailbox problem, motivated by the interaction between devices and processor in a computer. In this problem, a postman delivers letters to the mailbox of a housewife and uses a flag to signal a non-empty mailbox. The wife must remove all letters delivered to the mailbox and should not walk to the mailbox if it is empty. We present algorithms and an impossibility result for this problem.