Internal prioritization agent: This agent is triggered on the OnResolvedMessage event and assigns a lower priority to messages from the same sender that have a high accumulated cost. To support this functionality, Exchange 2013 uses the following mechanisms: For example, messages retain a setting of Important or Urgent, and so on. Messages still retain the original priority set by the user.
Message throttling doesn't affect the message priority from a user's perspective. This new behavior adds a "quality of service" aspect to the message throttling functionality in Exchange 2013. When a user repeatedly sends costly messages, such as messages that have large attachments or messages that are sent to many recipients, the Exchange 2013-based transport servers use a throttling policy to assign a lower priority to higher-cost messages from the user while continuing to deliver lower-cost messages.
This group of settings is known as a throttling policy. By using message costs, Exchange 2013 provides a group of settings that can control the effect that a user or connection has on an Exchange organization. This quality of service (QoS) feature was added in Microsoft Exchange Server 2010 SP1This cost is based on the following criteria:Įxchange 2013 transport servers track the average delivery cost of messages that are sent by individual users. To provide more consistent message throughput and predictable message delivery latency, Exchange 2013 establishes an accumulated cost for messages. When the utilization of the monitored system resources returns to normal levels, the server slowly increases the rate at which it accepts new connections and then establishes a normal level. When a monitored system resource, such as hard disk utilization or memory utilization, exceeds the specified threshold, the server reduces the rate at which it accepts new connections and messages, and focuses on delivering existing messages. Back pressure is a system resource monitoring feature in the Transport service on Mailbox servers and on Edge Transport servers. For more information about message size limits, see Message size limits.Īnother feature that helps avoid overwhelming the system resources of an Exchange transport server is back pressure. In addition to message throttling, you can also put size limits on the individual components of messages, such as the number of recipients, the size of the message header, or the size of individual attachments. Although a large backlog of messages and connections may be waiting to be processed, the message throttling limits enable the Exchange server to process the messages and connections in an orderly manner. These limits work together to protect an Exchange server from being overwhelmed by accepting and delivering messages. Message throttling involves a variety of limits on message processing rates, SMTP connection rates, and SMTP session time-out values. These limits prevent the accidental or intentional exhaustion of system resources on the Exchange server. Message throttling refers to a group of limits that are set on the number of messages and connections that can be processed by a Microsoft Exchange Server 2013 computer.
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