Microsoft SMTP Virtual Server does the following to messages that cause errors during processing. Each SMTP Virtual Server moves such messages into its own Badmail folder. This article describes how to use a script to automatically delete files from the Badmail folders. The procedure eliminates the administrative overhead of manually deleting or archiving the files. Additionally, this procedure makes sure that the Badmail folders do not exceed specific size limits.

More information:
This script is designed to run as a scheduled event at non-peak-usage hours, when e-mail flow and network traffic are low. The script can be downloaded from the Microsoft Download Center.To download the BadMailAdmin.exe file, visit the following Microsoft Web site:
http://www.microsoft.com/downloads/details.aspx?FamilyId=782AAF0F-6239-40AD-ADDA-97863D852FF7&displaylang=en

Source: Microsoft

The Sender ID Framework is a protocol created to counter e-mail domain spoofing and to provide greater protection against phishing schemes by verifying an e-mail message's sender.
Domain spoofing refers to the use of someone else's domain name when sending a message and is part of the larger problem of spoofing (the practice of forging the sender's address on e-mail messages). Domain spoofing can also be used by malicious individuals in phishing scams, which try to lure consumers into divulging sensitive personal information by pretending the e-mail is from a trusted source, such as a consumer's bank. Disclosure of such information can lead to identity theft and other online consumer fraud.
The Sender ID Framework is designed to verify that each e-mail message originates from the Internet domain from which it claims to come based on the sender's server IP address. Eliminating domain spoofing will help legitimate senders protect their domain names and reputations, and help recipients more effectively identify and filter junk e-mail and phishing scams.

If you whant to know more about the subject, here are some links:

http://www.microsoft.com/mscorp/safety/technologies/senderid/technology.mspx http://www.microsoft.com/downloads/details.aspx?familyid=B7CE1CAC-D884-4216-82FE-379F875663FF&displaylang=en

You can also use a wizard to implemet your SPF: http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/