Non-existent recipients must not be blocked.

From Exchange 2010 Edge Transport Server STIG

Associated with IA controls: ECSC-1

SV-44060r1_rule Non-existent recipients must not be blocked.

Vulnerability discussion

SPAM originators, in an effort to refine mailing lists, sometimes use a technique where they first create fictitious names, and then monitor rejected emails for non-existent recipients. Those not rejected, of course, are deemed to exist, and are therefore used in future SPAM mailings. To prevent this disclosure of existing email accounts to Spammers, this feature should not be employed. Instead, it is recommended that all messages be received, then evaluated and disposed of without enabling the sender to determine recipients that are existing vs. non-existing.

Check content

Open the Exchange Management Shell and enter the following command: Get-RecipientFilterConfig | Select RecipientValidationEnabled If the value of 'RecipientValidationEnabled' is not set to 'False', this is a finding.

Fix text

Open the Exchange Management Shell and enter the following command: Set-RecipientFilterConfig -RecipientValidationEnabled $False

Pro Tips

Lavender hyperlinks in small type off to the right (of CSS class id, if you view the page source) point to globally unique URIs for each document and item. Copy the link location and paste anywhere you need to talk unambiguously about these things.

You can obtain data about documents and items in other formats. Simply provide an HTTP header Accept: text/turtle or Accept: application/rdf+xml.