Emails can be viewed from the Dashboard, under My Recent Communications.

or from the Records Page (Settings > Communications > Records)

The Status column will indicate if the email was sent, failed, delivered, or opened.

Status	Icon
Delivered Indicates the email was sent and it was accepted by the recipients email server
Sent Indicates the email was successfully sent.
Failed The email could not be delivered to the recipients email server. Common reasons: Recipient email address does not exist or typed incorrectly, Domain name does not exist, Recipient email server has completely blocked delivery
Opened Indicates the recipient has opened the email. This will only show if all images in the email are fully loaded or if a link within the email is clicked. This may vary depending on email hosts.