The Exchange send connector connections count must be limited.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
low	V-259679	SRG-APP-000247	EX19-MB-000126	SV-259679r961155_rule	2024-08-22	2

Description
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.

Description

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.

ℹ️ Check
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-Object -Property 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.

ℹ️ Check

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-Object -Property 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
Update the EDSP to specify the "MaxOutboundConnections" value. Open the Exchange Management Shell and enter the following command: Set-TransportService -Identity <'IdentityName'> -MaxOutboundConnections 1000 Note: The <IdentityName> value must be in quotes. or Enter the value as identified by the EDSP that has obtained a signoff with risk acceptance.