I keep asking users not to send attachments locally, just the link to where it resides on the file server, but they do not listen. Is there a way to change the Send To:Mail Recipient in Windows Explorer so it just sends the link instead of the file? I would then like to prohibit the ability to send attachments locally but would like to make laptop users an exception as they work offline.
Depending on your overall requirements for this project, you could consider using custom Outlook security features based on your definition of two group policies (GPOs) in Active Directory, one for all laptop users and one for all other users. Then you'll want to get yourself a copy of the Office XP or Office 2003 Resource Kit. These ship with ADM templates that can be applied to all your users through the GPOs to essentially block all Level 1 file extensions that you define -- essentially prohibiting users from attaching and viewing defined attachment types. You'll need to define all the file types that you wish to block. Note that by enabling this functionality you will also block your end user's ability to view or even be cognizant of any attachments sent to them by anyone on the internet -- customers or otherwise. You'll need to give some thought to the actual requirements and who these policies should apply to in your organization. Finally, in order for these administrative templates to work, your users will need to be using either an online Exchange mailbox or offline storage folders (OST). They cannot be using PSTs for mail delivery.
It might be simpler to just deploy some sort of archival solution that scans your Exchange servers nightly and moves attachments to users' home directories leaving a hyperlink to the attachment instead. A number of solutions exist. Do a search for "enforce mailbox data management" or "Exchange archive" to locate these using your favorite Internet search engine.