How to use specific folder names in the backup rules ???

Hello everyone :) , i work in an IT department in france and I need some help :

i am new to SC DPM : I have configured a server (under Hyper-V ) with Microsoft Data Protection Manager on it, i followed the instructions given by this TechNet link : https://technet.microsoft.com/en-us/library/hh758153.aspx . 

(SQL server is OK)

i did the DPM Agent deployment via SCCM on a VM collection just to make sure that the agent is working well and it is OK , the agents are listed on the DPM console . 

when i try to set up a new protection rule, i select my computer, i need to backup a folder wich contains the username : i.e. : on the computer named VM-W10 i need to backup 'c:\username' fodler but i can't use 'C:\%USERNAME%\' as folder path, and the  environement variable is not detected when i do this and on the agent ( computer side), it says that i cant synchronize, because there is no folder selected ...

anyone have an idea ?

moreover, i need to backup a folder inside the folder which contain the username : i.e. : I need to backup the 'C:\username\mail'  folder but we can't know in advance what is the name of the folder on C:\{username} on each computer who have the agent installed . 

sorry for my bad english if any ...