How to get log or copy of email of user accounts

Hi

I've a log of user accounts on this portal. I'm administrator of all this accounts. Now i want a log of the user email ... Like some user will send any email then i should have a information or a copy of the email that what is he sending.... in the email for the security of the company.

So favour me how can i get a log of user email accounts.

Thanks

Manish

+919990666870