Problem with Ajax'd Mail()

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I'm hoping someone can help figure out how to stop a message that  
appears to be generated by my web host when sending to an non-resolvable  
email address that is supported by my web host. Things work correctly  
when sending to an invalid e-mail address off my web host .

The message returned is
+:/home/xxxxxx/dead.letter...saved message in /home/xxxxxxx/dead.letter  
and it ends up before the data in my return statement which then fails  
when my AJAXed javascript chokes attempting to EVAL the result.

I've tried everything I know to capture, discard or suppress the mesaage  
including using
Ob_start() before the mail command
with an Ob_end_clean() prior to the return statement.

Here's what currently is coded that also does not work
#   kill error display if mail fails
    ini_set ( "display_errors", "0" );  #Also tried FALSE
    ini_set ( "error_reporting", 0);
    if (!@mail($visitormail, $subject, $notes, $hdrs))
        return "document.getElementById('result_msg').innerHTML=             \"Sendmail  
has failed.\";

I admit so being something of a PHP neophyte and any help with this  
issue would be appreciated.

Thank you

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