The Exchange Send connector connections count must be limited.

From Microsoft Exchange 2016 Mailbox Server Security Technical Implementation Guide

Associated with: CCI-001095

SV-95397r1_rule The Exchange Send connector connections count must be limited.

Vulnerability discussion

The Exchange Send connector setting controls the maximum number of simultaneous outbound connections allowed for a given SMTP connector and can be used to throttle the SMTP service if resource constraints warrant it. If the limit is too low, connections may be dropped. If the limit is too high, some domains may use a disproportionate resource share, denying access to other domains. Appropriate tuning reduces risk of data delay or loss.

Check content

Review the Email Domain Security Plan (EDSP). Determine the value for SMTP Server Maximum Outbound Connections. Open the Exchange Management Shell and enter the following command: Get-TransportService | Select Name, Identity, MaxOutboundConnections If the value of "MaxOutboundConnections" is not set to "1000", this is a finding. or If "MaxOutboundConnections" is set to a value other than "1000" and has signoff and risk acceptance in the EDSP, this is not a finding.

Fix text

Update the EDSP to specify the "MaxOutboundConnections" value. Open the Exchange Management Shell and enter the following command: Set-TransportServer -Identity <'IdentityName'> -MaxOutboundConnections 1000 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.

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