Something like this:
On July xxx, we received your reply to request for evidence. It usually takes 725 (or whatever) days to process such a case. However, because your case has been through preliminary processing, it will take another 725 days to process, blah, blah, blah.
Don't be supprised how stupid and ridiculus the message is. The most important point is that it confirms your reply to RFE was received by INS!!!