Exchange external/Internet-bound automated response messages must be disabled.

From Microsoft Exchange 2016 Mailbox Server Security Technical Implementation Guide

Associated with: CCI-001308

SV-95409r1_rule Exchange external/Internet-bound automated response messages must be disabled.

Vulnerability discussion

Spam originators, in an effort to refine mailing lists, sometimes monitor transmissions for automated bounce-back messages. Automated messages include such items as "Out of Office" responses, nondelivery messages, and automated message forwarding.Automated bounce-back messages can be used by a third party to determine if users exist on the server. This can result in the disclosure of active user accounts to third parties, paving the way for possible future attacks.

Check content

Open the Exchange Management Shell and enter the following command: Get-RemoteDomain | Select Name, DomainName, Identity, AllowedOOFType If the value of "AllowedOOFType" is not set to "InternalLegacy", this is a finding.

Fix text

Open the Exchange Management Shell and enter the following command: Set-RemoteDomain -Identity <'IdentityName'> -AllowedOOFType 'InternalLegacy' Note: The and InternalLegacy values must be in single quotes.

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