You can find a sendlog of all the emails sent from your site under Reports > Sent Items. You'll see who sent what sort of email to whom at what time.
The list can be filtered by users, items (e.g. quotes or orders), email status (either sent or draft) and the time period.
You can see the content of the email by clicking on the subject, attachments can be opened by clicking directly on them.
You can also filter the list by a specific document sent as an attachment by typing the document number in the Attachment ID field.