Distribution List and storage

Hi all,

I like to confirm something :

Imagine I have a Distribution List, there is 10 members inside this DL. If I send a 2mb file to this DL, will it used up 2mb of storage or 20mb of storage(10*2mb)? Will it consumes the storage of all 10 members?

I remember reading it many many years ago..

Any URL to proof my theory will be helpful, thanks.