Message size limits are an important mechanism to control mailbox sizes, guarantee service availability, and protect from potential DOS attacks. Another commonly asked question is about message size limits and the inability to send messages that are apparently within the maximum sizes configured. Let’s take a look at the message size settings in different places in Exchange 2010 and Exchange 2007.
The organizational send and receive size limits apply to all Exchange servers in the Organization. The default is 10MB.
You can modify the organizational message size limits using the Set-TransportConfig cmdlet from the Exchange shell:
Set-TransportConfig -MaxReceiveSize 40MB -MaxSendSize 40MB
In Exchange 2007 SP1 and later, you can also set the organizational message size limits using the EMCby going to Organization Configuration | Hub Transport | Global Settings tab | Transport Settings | properties | General tab.
Figure 1: Setting the organizational message size limits from the Global Settings tab in the EMC in Exchange 2007 SP1 and later
Receive Connector limit
Unlike Exchange SMTP Virtual Servers in Exchange Server 2003/2000, Exchange 2007′s Receive Connectors are only used to receive messages. The maximum message size limit can be different on different Receive Connectors on a Hub Transport or Edge Transport server. For example, a Receive Connector for inbound Internet mail may have lower message size limits, but you may want to allow larger messages on Receive Connector for authenticated senders or partners.
To modify the maximum message size on a Receive Connector using the Exchange console, selectServer Configuration | Hub Transport | select a Hub Transport server | Receive Connectors -> select a connector | Properties | General tab.
Figure 2: Setting the maximum message size on a Receive Connector
To set ReceiveConnector limit using the shell:
Set-ReceiveConnector “CONNECTOR NAME” -MaxMessageSize 40Mb
What’s a Unique Binding for a Receive Connector?
Exchange 2010 and Exchange 2007′s definition of a unique binding for a Receive Connector is different than Exchange 2003/2000.
Whereas the latter considers a unique combination of an IP address + TCP port number as a unique binding, and does not allow another SMTP Virtual Server to be bound to the same combination of IP address + port number, Exchange 2010/2007 view a combination of IP address + port number + RemoteIPRanges as unique. This allows you to create a Receive Connector using the same IP address + port number, but using different RemoteIPRanges to specify the remote hosts that can connect to it. For example, you can create a Receive Connector for a set of remote hosts and specify a different message size to allow those hosts to send larger messages, or to restrict them to smaller messages.
Send Connector limit
Send Connectors are used for sending outbound messages to the internet or particular address spaces (domains). Edge Transport servers also have a Send Connector to send inbound messages to Hub Transport servers in an AD Site. To modify the maximum message size on Send Connectors, selectOrganization Configuration | Hub Transport | Send Connectors -> select connector |Properties | General tab.
Figure 3: Setting the maximum message size on a Send Connector
To set SendConnector limit using the shell:
Set-SendConnector “CONNECTOR NAME” -MaxMessageSize 40Mb