If you configure your SMTP trafic right, then answer is YES it can protect incoming and outgoing e-mails. But it can't protect Exchange server directly!
For incoming mail to your Exchange server configure SMTP Proxy. You will need to set up your SMTP route tables to point to your Exchange server. Then tell your Exchange server to use the ASL box as a smarthost. This configuration is working for me; however I am having a problem with the SPAM filter. I currently have this option disabled and need to post the problem I have having. Hope this helps.
