Options for Configuring Priority Queuing
All configuration options for priority queuing are available in the EdgeTransport.exe.config application configuration file that is located in the C:\Program Files\Microsoft\Exchange Server\Bin directory. The EdgeTransport.exe.config file is an XML application configuration file that is associated with the EdgeTransport.exe file. EdgeTransport.exe and MSExchangeTransport.exe are the executable files that are used by the Microsoft Exchange Transport service. This service runs on every Hub Transport server or Edge Transport server. Changes that are saved to the EdgeTransport.exe.config file are applied after the Microsoft Exchange Transport service is restarted. The default value is enforced if either of the following conditions is true:
-
A configuration option is missing.
-
A configuration option is present and contains the default value.
The following example shows the typical structure of the EdgeTransport.exe.config file:
<configuration>
<runtime>
<gcServer enabled="true" />
</runtime>
<appSettings>
<add key=" Configuration Option " value=" Value " />
…
</appSettings>
</configuration>
You can add new configuration options or modify existing configuration options in the <appSettings> section. Many configuration options available are completely unrelated to priority queuing. Any configuration options that don't involve back pressure are outside the scope of this topic.
Enabling or Disabling Priority Queuing
The PriorityQueuingEnable parameter enables or disables priority queuing on a Hub Transport server. The default value is False. To enable priority queuing, set the PriorityQueuingEnable parameter value to True in the EdgeTransport.exe.config file and restart the Microsoft Exchange Transport service.
Configuring the Maximum Size of a High Priority Message
The MaxHighPriorityMessageSize parameter controls the maximum allowed size of a High priority message. The default value is 250 KB. If a High priority message is larger than the value of MaxHighPriorityMessageSize parameter, the message is automatically downgraded from High priority to Normal priority.
When you enter a value, qualify the value with one of the following units:
-
KB (kilobytes)
-
MB (megabytes)
-
GB (gigabytes)
The value of the MaxHighPriorityMessageSize parameter should be significantly less than the value of the MaxMessageSize parameter on the Set-TransportConfig cmdlet. The default value of the MaxMessageSize parameter is 10 MB. A smaller value of MaxHighPriorityMessageSize helps make sure of consistent and predictable delivery times for High priority messages.
Configuring the Delay Notification Time-Out Based on the Message Priority
After each message delivery failure, the Hub Transport server generates a delay delivery status notification (DSN) message and queues it for delivery to the sender of the undeliverable message. This delay DSN message is sent only after a specified delay notification time-out interval, and only if the failed message wasn't successfully delivered during that time. This delay prevents the sending of unnecessary delay DSN messages that may be caused by temporary message transmission failures.
The following table shows the delay DSN notification time-out options that are based on the message priority.
Delay DSN notification time-out options that are based on the message priority
|
Parameter name
|
Default value
|
| LowPriorityDelayNotificationTimeout | 8:00:00 (8 hours) |
| NormalPriorityDelayNotificationTimeout | 4:00:00 (4 Hours) |
| HighPriorityDelayNotificationTimeout | 00:30:00 (30 minutes) |
To specify a value for a delay notification time-out, enter the value as a time span: dd.hh:mm:ss, where d = days, h = hours, m = minutes, and s = seconds. If the value is less than 1 day, you can omit the day part of the time span.
Configuring the Message Expiration Time-Out Based on the Message Priority
The message expiration time-out specifies the maximum length of time that a Hub Transport server tries to deliver a failed message. If the message cannot be successfully delivered before the expiration time-out interval has passed, a non-delivery report (NDR) that contains the original message or the message headers is delivered to the sender.
The following table shows the message expiration time-out options that are based on the message priority.
Message expiration time-out options that are based on the message priority
|
Parameter name
|
Default value
|
| LowPriorityMessageExpirationTimeout | 2.00:00:00 (2 days) |
| NormalPriorityMessageExpirationTimeout | 2.00:00:00 (2 days) |
| HighPriorityMessageExpirationTimeout | 8:00:00 (8 hours) |
To specify a value for a message expiration time-out, enter the value as a time span: dd.hh:mm:ss, where d = days, h = hours, m = minutes, and s = seconds. If the value is less than 1 day, you can omit the day part of the time span.
Configuring the Maximum Number of Connections Per Domain Based on the Message Priority
The maximum number of connections per domain specifies the maximum number of connections that a Hub Transport server can have open to any single remote domain. The outgoing connections to remote domains occur by using the remote delivery queues and Send connectors that exist on the Hub Transport server.
The following table shows the maximum number of connections per domain options that are based on the message priority.
Maximum number of connections per domain options that are based on the message priority
|
Parameter name
|
Default value
|
| MaxPerDomainLowPriorityConnections | 2 |
| MaxPerDomainNormalPriorityConnections | 15 |
| MaxPerDomainHighPriorityConnections | 3 |
The sum of the MaxPerDomainLowPriorityConnections parameter, the MaxPerDomainNormalPriorityConnections parameter, and the MaxPerDomainHighPriorityConnections parameter should be less than or equal to the value of the MaxPerDomainOutboundConnections parameter on the Set-TransportServer cmdlet. The default value of the MaxPerDomainOutboundConnections parameter is 20.