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