Moderators can use the workspace's "Email to Workspace" setting to direct content sent to the workspace via email to a certain folder in the workspace. If this is not set, all content sent in via email will be added to the workspace, but it will not be inside any particular folder.
First, visit the workspace you want to set this for, and click Settings to get to the workspace settings.
Then, select the email to workspace setting on the left hand side.
Finally, select the folder you want the content to go into, and click save to set your changes.