If you are so strong about not using any other mailing modules suggested by others, then you might have to change your script.After receiving this line

$formContents = param('formField');
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you should do some regex and remove the previous forward headers.If you could post the headers you currently receive in the mail I can suggest some Regex.But mind this:even after removing the previous headers, you cannot completely get rid of the mail header because the lines

print MAIL "To: $toEmail\n";
print MAIL "From: $fromEmail\n";
print MAIL "Subject: $formSubject\n";
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by themselves become a header.