Stop Producing Backscatter Spam (Exchange 2003/2007)
Back-scatter spam is when a server generates a bounce NDR email that is sent to a forged email address in response to receiving spam-email sent to an email address that does not exist, usually intentionally.
Disable the sending of NDRs and bounce incorrectly addressed emails at the MTA level
Perform the steps below and a server that attempts to send email to your server with an incorrect to-address will be rejected during the SMTP session (at the MTA level) and no NDR/bounce will be generated:
- Open Exchange System Manager: Go to Start > Programs > Microsoft Exchange > System Manager.
- Expand Global Settings, right-click Message Delivery and choose Properties.
- Under the Recipient tab check the Filter recipients who are not in the Directory check-box.
To ensure your SMTP server applies these settings:
- Expand the Exchange server that send emails to the internet under Administrative Groups, First Administrative Group, Servers
- Expand Protocols, SMTP, right-click Default Virtual SMTP Server and choose Properties.
- Under the General tab click Advanced.
- Click Edit and check the Apply Recipient Filter check-box
- Restart the SMTP service:
- Start > Run > cmd
- net stop "Simple Mail Transfer Protocol (SMTP)"
- net start "Simple Mail Transfer Protocol (SMTP)"
Issue the following cmdlet from within the Exchange Management Shell:
Set-RecipientFilterConfig -RecipientValidationEnabled $true