Ai, that is bad luck I would say slim chances to get it back, unfortunately. Perhaps it would be a good idea to do a remote wipe of the device, so your data is safe. (Well..not abused by anyone who finds the device).

Just a quick note: Read receipt is something invented by Microsoft, and pretty much only works with Outlook. If AF uses different software to manage emails (And I assume they do), read receipts will never 'fire', even if they did read your message.