If you're the administrator of a Dropbox for Business account, you can control whether team members can share stuff with people outside the team.
To set sharing permissions, sign in to the Dropbox website and click on Admin Console in the sidebar on the left. Then click on Sharing.
You can set different rules for shared folders and shared links. The rules will apply for everyone on the team, so you won't need to spend time making a decision about each instance of sharing. If you do allow sharing outside the team, members will still be able to make individual folders or links "team only" as needed.
The rules you set for shared folders do not apply retroactively. For example, if a team member invites someone outside the team to join a folder on Monday, then on Tuesday you turn off permission to invite outsiders to shared folders, the non-team member who got the invitation on Monday will still be able to join the folder.
Choose whether people outside your team can view shared links created by team members. If you allow this, a team member who creates a link can decide whether it's accessible to anyone or just the team.
Your setting for shared links does apply retroactively. If you don't allow links to be shared outside your team, any previous links that team members have created will no longer be viewable by outsiders. If you then allow links to be shared outside your team, those links will become viewable by outsiders again.
Note: Your setting only applies to shared links created by members of your team. If someone outside your team belongs to one of your shared folders and creates a link to the folder or any of the files, the link will continue to work regardless of your permission setting.
This article refers to a feature unique to Dropbox for Business. Dropbox for Business is designed for projects, groups, and other organizations that want to share the same Dropbox storage quota with all of its members. If you're interested in learning more or want to sign up, visit the Dropbox for Business webpage.