With the spread of low-cost computer systems and Internet connectivity@ the demand for local mail servers has been rising. Many people now want to operate a mail server on a system which has only an intermittent connection to a service provider. If the system has a static IP address@ the ESMTP ETRN command [ETRN] can be used. However@ systems with dynamic IP addresses (which are very common with low-cost connections) have no widely-deployed solution.