If the email is being sent to some addresses, but not others, the SMTP server is refusing to relay to those addresses for some reason. contact the host and see if they can can look into the SMTP server error logs, there are likely some clues into why the SMTP server is not relaying to those addresses in the errors logs.
To have a copy of every order sent to you, add your address to the $WAGLOBAL_Receipt_Email_BCC variable in the WA_Globals.php file.