Hey Ian -- There's actually a lot that might have happened here. It can be that you are using a free domain(google.com30 or yahoo.com24) as it has a tendency for the email to not arrive or land in the spam folder. or the subscriber has a strict domain setting that prevents their inbox provider to receive emails from you. You can either reach out to your subscribers outside CK and request to allowlist your sending email address, or you might need to reach out to ConvertKit support so that they can check out what happened. You can reach their support here: https://convertkit.com/support32

Robert
Free Diver | Adventurer