First, from your E-junkie Dashboard go to View/Download Logs > Transaction Log and see if you can find the affected sale. If it does not appear there, we have not yet received confirmation of payment from the payment processor, so our system has no way of knowing the order was actually placed.
Double-check every step of our integration procedure for the payment service where you received the affected buyer's payment, to make sure you haven't overlooked anything or made any mistakes; our integration page for each payment service also includes a Troubleshooting section near the bottom with links to additional information (e.g., for PayPal).
If you can find the affected order in your E-junkie Transaction Log, that confirms we did process that order, so you can check if Sale Notification emails are enabled for your account. Click the Try New Features button in the top header of your E-junkie Dashboard (or just click here while logged in), then under New Sales Notification on the screen that comes up, if you see a green Enable button there, click that to re-enable your Sale Notification emails.
If you instead see a red Disable button there, that confirms Sale Notifications are enabled, so look in your spam folder to see if your email provider has mistaken the missing Sale Notification email for spam; if you find the message there, be sure to mark it as Not Spam, and it may be a good idea to add
to your spam filter's whitelist (if you have one) as well as your address book or contact list, to help ensure delivery of notifications from our system in the future.