2.2.5 Ensure 'Maximum receive size: Connector level' is set to '25'

Information

This setting limits the size of a message a user can receive. Receive size includes the header This includes the message header, the message body, and any attachments. For internal message flow, Exchange Server uses the custom X-MS-Exchange-Organization-OriginalSize message header to record the original message size of the message as it enters the Exchange Server organization. Whenever the message is checked against the specified message size limits, the lower value of the current message size or the original message size header is used. The size of the message can change because of content conversion, encoding, and agent processing.

Rationale:

This setting somewhat limits the impact a malicious user or a computer with malware can have on the Exchange infrastructure by restricting the size of incoming messages.

Impact:

Users will not be able to receive messages larger than the limit.

Solution

To implement the recommended state, execute the following PowerShell cmdlet:

Set-ReceiveConnector 'Connection from Contoso.com' -MaxMessageSize 25MB

To set MaxMessageSize on all receive connectors this command can be executed:

Get-ReceiveConnector | Set-ReceiveConnector -MaxMessageSize 25MB

OR

Perform the following actions:

Launch the EAC (Exchange Administrative Center).

Go to 'Mail Flow' on the left and click on the 'Receive Connectors' tab.

Double-click on the receive connector to be modified.

Change the Maximum receive message size (MB): to25and click Save.

Default Value:

36 MB (37,748,736 bytes)

See Also

https://workbench.cisecurity.org/benchmarks/12442

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-5

Plugin: Windows

Control ID: 3e2b9a5c82e04b6f5fbee2fac3384c788ce9a13cd788b6352a9b1e7b0caf6aef