MPPE stands for Microsoft Point to Point Encryption. MPPE is used to encrypt data traveling over a PPTP, or Point to Point Tunneling Protocol, connection.
When setting up a PPTP connection using DD-WRT firmware on your router there is a blank field to configure MPPE Encryption options in the VPN/PPTP setup. By default the text “mppe required” is typed into this field. You can add a couple other options which include no40, no56, and stateful or stateless. Descriptions of these options are listed below.