In order for this service to operate it must retain some information about files, who can access them, and what has happened. Files will be automatically removed from the system when they expire and other retained information will be removed from the system and database after some amount of time has passed. This page allows you to see how long various pieces of information are retained by this installation.
Note that when a transfer is deleted, all the related files are also deleted along with the copies of any emails that have been sent out which relate to the transfer.