You must purchase additional email activity history to gain access to the Email Activity Feed API.
The Email Activity API allows you to query all of your stored messages, query individual messages, and download a CSV with data about the stored messages.
Once retrieved, you can inspect the data associated with your messages to better understand your mail send. For example, you may retrieve all bounced messages or all messages with the same subject line and search for commonalities among them.
See "Getting Started with the Email Activity Feed API" for help building queries and working with the API.
You can also work with email activity in the Activity section of the Twilio SendGrid App.