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V-259684

CAT III (Low)

The Exchange Outbound Connection Limit per Domain Count must be controlled.

Rule ID

SV-259684r961155_rule

STIG

Microsoft Exchange 2019 Mailbox Server Security Technical Implementation Guide

Version

V2R3

CCIs

CCI-001095

Discussion

Email system availability depends in part on best practice strategies for setting tuning configurations. This configuration controls the maximum number of simultaneous outbound connections from a domain as a delivery tuning mechanism. 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. By default, a limit of 20 simultaneous outbound connections from a domain should be sufficient. The value may be adjusted if justified by local site conditions.

Check Content

Review the Email Domain Security Plan (EDSP) or document that contains this information.

Determine the value for Maximum Outbound Domain Connections.

Open the Exchange Management Shell and enter the following command:

Get-TransportService | Select-Object -Property Name, Identity, MaxPerDomainOutboundConnections

If the value of "MaxPerDomainOutboundConnections" is not set to "20", this is a finding.

or

If "MaxPerDomainOutboundConnections" is set to a value other than "20" and has signoff and risk acceptance in the EDSP, this is not a finding.

Fix Text

Update the EDSP to specify the "MaxPerDomainOutboundConnection" value or verify that this information is documented by the organization.

Open the Exchange Management Shell and enter the following command:

Set-TransportService -Identity <'IdentityName'> -MaxPerDomainOutboundConnections 20

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.