The Exchange Global Recipient Count Limit must be set.

From MS Exchange 2013 Mailbox Server Security Technical Implementation Guide

Part of SRG-APP-000261

Associated with: CCI-001308

SV-84669r1_rule The Exchange Global Recipient Count Limit must be set.

Vulnerability discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. The Global Recipient Count Limit field is used to control the maximum number of recipients that can be specified in a single message sent from this server. Its primary purpose is to minimize the chance of an internal sender spamming other recipients, since spam messages often have a large number of recipients. Spam prevention can originate from both outside and inside organizations. While inbound spam is evaluated as it arrives, controls such as this one help prevent spam that might originate inside the organization. The Recipient Count Limit is global to the Exchange implementation. Lower-level refinements are possible; however, in this configuration strategy, setting the value once at the global level facilitates a more available system by eliminating potential conflicts among multiple settings. A value of less than or equal to 5000 is probably larger than is needed for most organizations but is small enough to minimize usefulness to spammers and is easily handled by Exchange. An unexpanded distribution is handled as one recipient. Specifying “unlimited” may result in abuse.

Check content

Review the Email Domain Security Plan (EDSP). Determine the global maximum message recipient count. Open the Exchange Management Shell and enter the following command: Get-TransportConfig | Select Name, Identity, MaxRecipientEnvelopeLimit If the value of MaxRecipientEnvelopeLimit is not set to 5000, this is a finding. or If the value of MaxRecipientEnvelopeLimit value is set to an alternate value and has signoff and risk acceptance in the EDSP, this is not a finding.

Fix text

Update the EDSP. Set-TransportConfig -MaxRecipientEnvelopeLimit 5000 or The value as identified by the EDSP that has obtained a signoff with risk acceptance. Restart the Microsoft Exchange Information Store service.

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