Exchange Message size restrictions must be controlled on Send connectors.

From Microsoft Exchange 2016 Mailbox Server Security Technical Implementation Guide

Part of SRG-APP-000247

Associated with: CCI-001095

SV-95395r1_rule Exchange Message size restrictions must be controlled on Send connectors.

Vulnerability discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. For message size restrictions, multiple places exist to set or override inbound or outbound message size. Failure to control the configuration strategy can result in loss of data or system availability. This setting enables the administrator to control the maximum message size on a Send connector. Using connectors to control size limits may necessitate applying message size limitations in multiple places, with the potential of introducing conflicts and impediments in the mail flow. Changing this setting at the connector overrides the global one. Therefore, if operational needs require it, the connector value may be set lower than the global value with the rationale documented in the Email Domain Security Plan (EDSP).

Check content

Review the Email Domain Security Plan (EDSP) or document that contains this information. Determine the maximum message send size. Open the Exchange Management Shell and enter the following command: Get-SendConnector | Select Name, Identity, MaxMessageSize For each Send connector, if the value of "MaxMessageSize" is not the same as the global value, this is a finding. or If "MaxMessageSize" is set to a numeric value different from the maximum message send size value documented in the EDSP, this is a finding.

Fix text

Update the EDSP to specify the "MaxMessageSize" value or verify that this information is documented by the organization. Open the Exchange Management Shell and enter the following command: Set-SendConnector -Identity <'IdentityName'> -MaxMessageSize Note: The value must be in single quotes. or Enter the value as identified by the EDSP that has obtained a signoff with risk acceptance. Repeat the procedures for each Send connector.

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