Non-existent recipients must not be blocked.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
Exch-ED-227	Exch-ED-227	Exch-ED-227_rule		Medium

Description
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.

Description

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.

STIG	Date
Microsoft Exchange 2010 Edge Transport Server Role	2012-05-31

Details

Check Text ( C-_chk )
Open the Exchange Management Shell and enter the following command. Get-RecipientFilterConfig \| Select RecipientValidationEnabled If the value of "RecipientValidationEnabled" is set to "False", this is a finding.

Fix Text (F-_fix)
Open the Exchange Management Shell and enter the following command. Set-RecipientFilterConfig -RecipientValidationEnabled $False