BAD file format is used by Microsoft Exchange Server, an email and calendaring server. BAD files are used for storing messages not yet sent by the server to recipient for various reasons. BAD files contains exact copy of the original message.

Microsoft Exchange Server save BAD files is ‘Badmail’ folder. Such files can be viewed again by transferring to ‘Pickup’ folder and opening them. System administrators sometimes used scritps to automate ‘Badmail’ folder pruning.