I have QC 5.x freshly installed through softacolous from cpanel.
The problem is that the admin (me - 1stemail@gmail.com) did not received any email but the customer (me also but another email - 2ndemail@gmail.com) did received "Thank you email" from 1stemail@gmail.com via SSL outgoing mail server.
I am sorry for the trouble. QC actually did send the order email. It just ended up in spam folder. No matter how many time I clicked "Not Spam" in Gmail, it still end up in spam folder because the @gmail.com email was sent through the SSL server not through gmail.
Thanks!
p/s: I think when people complaint that they are not receiving order email the quick answer is to ask them to check spam folder especially when they use @gmail.com for the administrative email.