Visit the campaign dashboard screen to view the 'Response Rate Graph'. If you hover over the current day, it will tell you how many emails you have sent within this campaign. If you click on this dot, you will be taken to your All Emails folder.
You can also access this information by visiting your All Emails folder. This will show every email you’ve sent and received, broken down into several categories: 'Inbound', 'Outreach Emails', 'Sent Replies', 'Scheduled Replies' and 'Snoozed' in the drop-down menu. Select the 'Outreach Emails' option to see all of the outreach emails (1st, 2nd, and 3rd attempts), starting with the most recent.