This post discuss an ability to send email from the Internet to a SharePoint document library running on SBS 2008. The steps on how to set this up are all documented under method 2 from the previous post. After you create the new mail contact, the Windows SBS Email Address Policy will stamp the contact with the external SMTP address as a secondary address. When you send an email to this SMTP address, the Exchange Transport service will deliver to the primary SMTP address. In the example above, if I send to mylist@contoso.com, Exchange will deliver to mylist@companyweb. At that point the email is forwarded to the drop directory, picked up by Sharepoint, and the attachments are delivered to the “mylist” document library.

Source:→ SBS Blog