I have an intended unique constraint on a custom field in a Case.  The intent is to prevent duplicate similar cases from entering the system.

It pretty much works as expected, I only get one Case record for the each unique key, regardless of how many web-to-case submission.

The problem is that for each duplicate submission, I get multiple emails sent to me.  One almost imediatly, one a few hours later, then one a day later.

How can I turn this behavior off?  Or at the minimum, add useful information to the email indicating that it is a "duplicate" email.
Would turning off "debug" or not sending "debugemail" turn this off?  I can't find any documentation regarding these hidden fields.

Here's a sample email content:
Email Subject: Salesforce Case Alert
Sender: QA_SUPPORT@salesforce.com
Content:

Alert:  Salesforce experienced the following problem creating the case below:

Reason: common.exception.UniqueConstraintViolationException: java.sql.SQLException: ORA-00001: unique constraint (CORE.AK2CUSTOM_UNIQUE_VALUE) violated
ORA-06512: at "SLEEPY.CCUSTOMFIELDDATA", line 362
ORA-06512: at "SLEEPY.CCUSTOMFIELDDATA", line 192
ORA-06512: at "SLEEPY.CCUSTOMFIELDDATA", line 30
ORA-06512: at "SLEEPY.CCUSTOMFIELDDATA", line 1640
ORA-06512: at "SLEEPY.TCASE", line 1178
ORA-06512: at "SLEEPY.TCASE", line 1287
ORA-06512: at line 1
: {call tCase.insert_detail(?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)})}

Record Information:

    00NC00000011axi = test@test.com
    debug = 1
    debugEmail = xxxmyemailxxx
    description = assdf2
    email = test
    encoding = UTF-8
    external = 1
    name = Test
    orgid = 00DC0000000DRf1
    phone = 1234
    retURL = http://
    subject = Test
    submit = Submit Query

To incorporate this case into Salesforce you can key in the data above.

If you have any questions, please click on Help & Training at the top right of any page within Salesforce.

Thank you!

Customer Support
salesforce.com, inc.
The Landmark @ One Market, Suite 300
San Francisco, CA 94105
Email: QA_SUPPORT@salesforce.com
Phone: (415) 901-7010
Fax: (415) 901-5593