How do I see the Messages that have been sent?

To review the Messages that have been sent out from anywhere in the Organization, view the Email History list found within the Email Communications tab. 

email hist org

From here you can see the entire list of the Messages that have been sent out at the Organization level, as well we all Opportunities.

Tip: Bounce lists display which people met the send criteria but were unsubscribed and thus were not sent the communication. 

The main list view provides an overview of each Message, and there is also a details pop-up that will provide more specific details on the recipients, deliveries, and bounce rates. From the detailed pop-up, you are also able to preview the message that was sent. 

email hist org details