No emails being sent with orders, how do I fix that?

I've got a couple of things for sale on heartsandlaserbeams.com, and when folks buy the ebook, I'm getting emails from customers that they're not receiving an email with a download link. I wasn't receiving any email notifications about any orders from the Marketpress plugin, either. I just get the paypal notification that there's been a purchase.

How do I get those notification emails to send?

Interesting side note - I just bought an ebook from myself to make sure customers were really not getting an email, and I did not receive the email with the download link as the customer. But that time, I DID receive a notification from the plugin as the seller that there was an order in my shop.