You can review which messages were sent AND to whom you sent them. Click Messages from the main menu, then Viewing Sent Messages and the following screen will appear:

Again, the messages are sorted in descending order, so the most recent message is on top. To view the message itself, click View next to the message you want to see. It will display the same way messages appear when you receive them (except you won't be able to mark sent message as unread!)

To see who you sent the message to, click Recipients and the following screen will appear:

On this screen, the subject of the message appears at the top, along with the list of the recipients AND the date they read the message (or unread if they have not yet read it.) Note that even though you may have selected a group, rather than individuals, the recipient list will always be shown as each individual that was sent the message.