When emailing file attachments into a Box folder, Box also includes undesirable files such as logos, signature images, etc. The logo and related files are not consistently named so you cannot select a specific file to delete. Could you modify Box Relay so that users could delete these files in a named folder using the wildcard function i.e. .PNG?
So it would be Action=A File Action, Delete. Then the user would identify the folder where to delete and select a new option named "delete by file name". There the user would enter ".PNG" or something similar.