Details

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.

Solution

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.

Supportive Information

The following resource is also helpful.

• https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_MS_Exchange_2016_Y21M07_STIG.zip

This security hardening control applies to the following category of controls within NIST 800-53: System and Communications Protection.This control applies to the following type of system Windows.

References

• 800-53|SC-5(2)
• CAT|III
• CCI|CCI-001095
• Rule-ID|SV-228386r612748_rule
• STIG-ID|EX16-MB-000420
• STIG-Legacy|SV-95397
• STIG-Legacy|V-80687
• Vuln-ID|V-228386

Source

• Tenable.com/audits