I have a client using Windows Mail on a Surface Pro tablet running Windows 8.1. From the Windows Mail client, they are unable to send messages with attachments greater than 5 MB in size. If I have them send via Outlook, there's no issue. Based on the Transport Settings configured on our Exchange server, we should be able to send a 50 MB attachment.

Does anyone know of a registry key that can be added (similar to the one for Outlook) that will configure Windows Mail to allow for larger attachments?