You can check the email history for any of your tours within the Email History tab of the tour editor.
The history will show you when the email was sent, who the recipient was, the Subject of the email, as well as the status and if it has been opened by the recipient.
If the status is Rejected / Bounced / Failed, you will receive an email notification letting you know the email bounced, along with a bounce reason.
If needed, you can resend emails to your customers.
You can resend the Stats email immediately from the Stats tab.
You can also resend the Tour Announcement email directly within the Delivery Manager.
You can resend the Client Panel Invite directly within the Customer account.
If these aren't solving your issue, take a look at our guide to improving email deliverability.