Delivery Class Message Throttling policies in Exchange Server 2010 SP1

Exchange Server 2010 uses throttling policies to limit the number of RPC requests from clients which could cause performance problems. Concurrent connections restrictions can be applied to Exchange Web Service, POP3/SMTP, OWA, ActiveSync and Remote PowerShell.  Only the policies limiting concurrent connections were enabled by default in Exchange 2010 RTM, but in Exchange 2010 SP1, all clients throttling policies are enabled by default.

Exchange Server 2010 SP1 also adds new feature called, Delivery Class Throttling where messages can be classified based on certain characteristics and accordingly assign it a delivery class. Cost is assigned to each message based on message size, number of recipients and frequency. This cost factor is then used to assign a delivery class to the messages. Message priority is measured according to their class, which means the higher the delivery class, the higher the message priority is in the connector queue. For example, delivery class throttling will give high priority to small messages with few recipients over bulk messages with many recipients in the message queue.