Find number Of email send and received per day

HI All,

 I want to decommissioned my Exchange Server. But i want to know how many users are  still send and received. 

 findout number of items they've sent in say the last 2 weeks.

  Logging into their mailbox won’t tell us anything as they’re still meant to be doing this for “history”, however if they’re sending from it then it may tell us something.

AS