You can check the Delivery Status using the Email and Mail Register views from Documents and Clients - Documents list. Refer to Emails Sent, Received and Draft and Mail Register Views.
Also, in the Activity section in the Drawer, this shows "Marked as Sent" with the date and time and the person who sent it.
Resending an Email or Document
If you need to resend a document by email at any time, you can do so with the Send button. Refer to the section Sending Documents to Clients.
If you need to resend an email, you can do this in the same way as resending a document.