The DoD has provided network storage for every employee. Everyone has access to information on how to use this storage area for individuals or small groups. Programs within private industry that do business with the DoD or contract to support the DoD have access to DoD sponsored tools or program sponsored sharing websites. No email attachments should be allowed. If someone needs to gain access to information in a file, it should be posted to one of these resources and then accessed by the receivers.
Email attachments create unnecessary redundant costs for server space, hard disk space, and email backup. It also is a security risk because email can be forwarded to others or intercepted.
Ignorance about how to use these network resources for sharing information can be cured very quickly if a DoD wide policy is enforced that explicilty disallows email attachments.
Example: On any given day, if only 100,000 emails with a 1 MB attachment sent to an average of 6 people, costs a half Terabyte of server space on the DoD email system which by law must also be backed up. Then the file is saved by all recipients on their local storage. By copying the file to the network (one copy instead of six) would shift the cost to the network resources (~100 GB) but these resources are also limited and so must be deleted by the originator. So the temporary nature of the file transfer versus the persistent backup of email will save thousands of dollars a day in network area storage costs DoD wide.
The infrastructure and mechanisms are in place already - to implement this cost savings, it only requires a flow down of policy. An email perhaps.