My customers aren't getting website order notifications, what's going on?

It is likely that a major email provider, such as AOL or Gmail, has blacklisted you somehow and is blocking email from your domain to all of their users. If you can identify which services are blocking you (check the emails of the customers that have reported they're not getting your email), you can send requests to their support to remove you as a spammer. Just send an email to, for example, support@gmail.com, with the subject 'Please Whitelist mystorename.com', and in the message, explain that you are a legitimate business and should not be blocked from emailing your customers and subscribers.