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Exchange Server Compatibility Information Exchange Server Version Compatibility 5.5 No 2000 No 2003 No 2007 Yes

Filter Out Mail to Non-Existent Users - Exchange 2007
Author: Simon Butler, Exchange MVP, MCSE

This is for Exchange 2007 ONLY. For the version for Exchange 2003, click here: Filter Out Mail to Non-Existent Users - Exchange 2003

Exchange 2003 introduced a new facility to filter email messages if the email address do not exist in the Active Directory. This stops spammers from sending messages to non-valid addresses. 

The rejection is done at the SMTP level - so the email message isn't even delivered. If valid senders misspell an email address then they will get a bounce message immediately - indicating that the message has been rejected.

The ability for Exchange 2007 to drop email for unknown recipients is also available as part of the anti-spam functionality. but is not enabled by default. The management control for anti-spam is only installed by default on the Edge role, for other roles (for example on a single server deployment) the anti-spam functionality needs to be installed by running a script.

Anti-spam Controls Installation.

1. In The Exchange Management Shell, change to the following directory (presuming default installation location) C:\Program Files\Microsoft\Exchange Server\Scripts
2. Use tab to select install-AntispamAgents.ps1 and press enter.
3. Once it has completed, restart the Exchange Management Console and go in to Organisation Configuration, Hub Transport and select the Anti-spam tab.
   If you cannot see the Anti-Spam tab then close the console and restart the Microsoft Exchange Transport Service.

Enable Recipient Filtering.

1. All of the anti-spam options are enabled by default. For now, disable them all except for recipient filtering.
2. Go in the the properties of recipient filtering and enable the option "Block messages sent to recipients not in the global address list" on the Blocked Recipients list. Apply/OK out.
3. Restart the Microsoft Exchange Transport Service again.

Tarpit

With Exchange 2003 you needed to enable the tarpit to protect against directory harvest attacks. That is not required with Exchange 2007 as tar pit is enabled by default.