Inbox placement rate - aka: IPR - is a key email deliverability metric which measures what percentage of sent emails reach recipients’ inboxes.
Inbox placement rate = Inbox placements / total email sent
Emails sent = Inbox placements + emails blocked + emails filetred to junk or spam folder
Inbox placement rate is often seen as more accurate and pertinent than the classic deliverability rate.
IPR for US market in 2012
Image credit: Return Path "The email intelligence reporte Q3 2012".
See also average inbox placement rate.