Email Blacklist REgular Expression Rejecting A Domain That Is Not On The Blacklist

I am using a regular expression to validate email addresses and not accept an email address from a domain identified as providing a free email service.  This is done based on the domain name in the email address.

The problem is that a valid email address (valid domain) is being rejected as invalid.

"usa.com" is a domain that is included on the blacklist.

 "dccusa.com" is being rejected, even though it is not on the blacklist.  I assume this is because it contains the domain "usa.com" which is on the blacklist.

Here is my test code:

<script language="JavaScript" src="blacklist.js"></script>
<SCRIPT LANGUAGE="JavaScript">
        var blacklist = new RegExp(blacklist.join("|"));
       var emailVar = "test@dccusa.com";
         if(emailPart=emailVar.match(/^\w+([\-\.]\w+)*\@(\w+([\-\.]\w+)*\.[a-z]{2,4})$/)){
                 if(blacklist.test(emailPart[2])){
                       alert("It appears that you have entered an email address from a free email service provider.
                  Unfortunately, we do not accept registrations from these email addresses.  Please enter a
                  different email address or call for assistance.");
                 }
         } else {
                alert("Please enter valid email address.");
         }
        alert ("The End.")

</script>

The following is what a segment of the blacklist looks like:
...
,"post.com"
,"sanfranmail.com
,"soon.com"
,"usa.com"
,"yours.com"
,"saudia.com"
,"terra.com.br"
,"uol.com.br"
,"yahoo.com"
...

What can I do so that "dccusa.com" will not be rejected as a valid domain for email?