Each reservation has a "guest emails" section. In this section - you can view when an email was sent and if it was rejected/bounced.
Example: Confirmation and cancellation both sent
Example: Emails bounced/rejected by recipient's email provider. Double check the address with the guest.
Troubleshooting Guest Emails
In some situations - even though the email was sent it doesn't mean it was delivered or that the guest received it. Their inbox may have sent the message to spam/junk, or the email address may be incorrect. If the guest did not receive your emails double check the email address with them.
You can always update the email address, save the reservation with the new address and then re-send a confirmation email to reset