Configuring Messaging Limits for the Pickup Directory
You can set messaging limits
for the Pickup directory for message header sizes and maximum
recipients per message. The default message header size is 64 KB. To
change this setting, you can set the –PickupDirectoryMaxHeaderSize
parameter of the Set-TransportServer cmdlet to the desired size. The
valid input range for this parameter is 32,768 to 2,147,483,647 bytes.
When you specify a value, you must qualify the units for that value by
ending with one of the following suffixes:
-
B for bytes
-
KB for kilobytes
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MB for megabytes
-
GB for gigabytes
The following example sets the maximum header size to 256 KB:
Set-TransportServer -Identity MailServer48
-PickupDirectoryMaxHeaderSize "256KB"
The default maximum recipients per message
is 100. To change this setting, you can set the
–PickupDirectoryMaxRecipientsPerMessage parameter of the
Set-TransportServer cmdlet to the desired size. The valid input range
for this parameter is 1 to 10,000. The following example sets the
maximum recipients to 500:
Set-TransportServer -Identity MailServer48
-PickupDirectoryMaxRecipientsPerMessage "500"
Configuring Message Throttling
Message throttling sets limits on the number of messages and connections that can be processed by a Hub or an Edge Transport server. These limits
are designed to prevent the accidental or intentional inundation of
transport servers and help ensure that transport servers can process
messages and connections in an orderly and timely manner. Throttling works in conjunction with size limits on messages that apply to header sizes, attachment sizes, and number of recipients.
On Hub and Edge Transport servers, you can set some message throttling options in the Exchange Management Console. You do this by using the options on the Limits tab in the transport server's Properties dialog box. In the Exchange Management Shell, you can configure all message throttling options by using Set-TransportServer and related parameters.
-
MaxConcurrentMailboxDeliveries
Sets the maximum number of delivery threads that can be open at the
same time to deliver messages to mailboxes. The default value is 30.
-
MaxConcurrentMailboxSubmissions
Sets the maximum number of delivery threads that can be open at the
same time to accept messages from mailboxes. The default value is 30.
-
MaxConnectionRatePerMinute
Sets the maximum rate at which new inbound connections can be opened to
any Receive connectors that exist on the server. The default value is
1,200 connections per minute.
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MaxOutboundConnections
Sets the maximum number of concurrent outbound connections that can be
open at the same time for Send connectors. The default value is 1,000.
-
MaxPerDomainOutboundConnections
Sets the maximum number of connections that can be open to any single
remote domain for any available Send connectors. The default value is
20.
With Set-SendConnector,
you can configure throttling by using ConnectionInactivityTimeOut. This
parameter sets the maximum idle time before an open SMTP connection is
closed. The default value is 10 minutes.
With Set-ReceiveConnector, you can configure throttling using the following parameters:
-
ConnectionInactivityTimeOut
Sets the maximum idle time before an open SMTP connection is closed.
The default value is 5 minutes for a Hub Transport and 1 minute for an
Edge Transport.
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ConnectionTimeOut
Sets the maximum time that an SMTP connection can remain open, even if
it is active. The default value is 10 minutes for a Hub Transport and 5
minute for an Edge Transport. ConnectionTimeout must be longer than
ConnectionInactivityTimeout.
-
MaxInboundConnection Sets the maximum number of simultaneous inbound SMTP connections. The default value is 5,000.
-
MaxInboundConnectionPercentagePerSource
Sets the maximum number of simultaneous inbound SMTP connections from a
single source server. The value is expressed as the percentage of
available remaining connections on a Receive connector (as defined by
the –MaxInboundConnection parameter). The default value is 2 percent.
-
MaxInboundConnectionPerSource
Sets the maximum number of simultaneous inbound SMTP connections from a
single source messaging server. The default value is 100.
-
MaxProtocolErrors
Sets the maximum number of SMTP protocol errors allowed before a
Receive connector closes a connection with a source messaging server.
The default value is 5.
-
TarpitInterval
Sets artificial delay in SMTP responses where unwelcome messages are
being received from anonymous connections. The default value is 5
seconds.
Understanding Back Pressure
Back pressure
limits overutilization of system resource on a Hub Transport or an Edge
Transport server. Transport servers monitor key system resources to
determine usage levels. If usage levels exceed a specified limit, the
server stops accepting new connections and messages. This prevents
server resources from being completely overwhelmed and enables the
server to deliver the existing messages. When usage of system resources
returns to a normal level, the server accepts new connections and
messages. Resources monitored as part of the back pressure feature include:
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Free space on hard disk drives that store the message queue database transaction logs.
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Free space on the hard disk drives that store the message queue database.
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The amount of memory used by all processes.
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The amount of memory used by the Edgetransport.exe process.
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The number of uncommitted message queue database transactions that exist in memory.
Levels of usage are defined as normal, medium, or high.
With the normal level, the resource is not overused, and the server
accepts new connections and messages. With the medium level, the
resource is slightly overused, and limited back
pressure is applied, allowing mail from senders in the authoritative
domain to continue being sent while the server rejects new connections
and messages from other sources. With the high level, the resource is
severely overused and full back pressure is applied, meaning message flow stops and the server rejects all new connections and messages.
You have limited control over how back
pressure is applied. Some related settings can be configured in the
Edgetransport.exe.config file on Edge Transport servers. However,
Microsoft recommends that you don't change the default settings.
