Edge Architecture Design Recommendations

• Capacity planning for the Edge tier is difficult to generalize. You should work with the hardware and software vendors who are supplying equipment for your deployment to develop a capacity plan. Nevertheless, you should implement the Realtime Blackhole List (RBL) at your site at the Edge tier. The RBL is a list of IP addresses whose owners refuse to stop the proliferation of spam.

• Design the Edge tier for minimal latency (less that one millisecond through the entire Edge tier).

• Use load balancing algorithms that are load-aware by CPU utilization or by the number of active connections. Round-robin is not an acceptable load-balancing model. With the exception of MTAs (stateless), use sticky-bit load balancing.

• Webmail clients need load balancers that can manage sticky bits, because Webmail interfaces do not share state across Webmail servers.