Lack of awareness about why campaigns didn’t succeed is a surprisingly common point of failure for email marketers. Many mistakenly assume that the subject line was the culprit or their lists are simply less engaged. The root cause is often something different, and luckily something that can be easily fixed — as long as marketers are aware of it: the inbox placement rate.

The inbox placement rate measures how many messages arrive in your subscribers’ inboxes — and not in spam folders or otherwise undelivered by the mailbox provider — giving marketers a more accurate base to measure subscriber engagement against.

Without this viewpoint, marketers can receive and act on misleading signals about their email campaign performance. Not knowing your inbox placement can invalidate everything you learn about three fundamental aspects of your email program: your program benchmarks, any tests you perform, and your overall email ROI.

Program Status
Your inbox placement rate acts as the foundation of all other email program metrics — everything is built from it. You won’t have a reliable view of your opens, clicks, and complaints until you know how much email is being seen by your subscribers. For example a recent campaign may have had really low open rates, leading you to decide that campaign was a bust and to try something else. Unbeknownst to you, your inbox placement rate at one or more mailbox providers was critically low. Had you known your low placement rate, you could have decided to re-send your campaign and re-measure results to see if engagement was low because few subscribers saw your messages.

Testing
Similar to misdiagnosing a campaign’s failure, if you are testing against a false benchmark, your interpretations of your test results will also be wrong. For example when trying out a new subject line through A/B testing, you could be unwittingly eliminating the worst-performing subject line because not everyone in your “losing” sample was receiving the message and therefore didn’t see it and couldn’t open it. By checking the inbox placement rates of all your campaigns you will have a more accurate measure of subscriber response.

ROI
Every campaign has a cost: the cost to deploy the email, the hours spent designing, writing, and coding the messages, etc. If you are unaware of inbox placement issues, not only are you wasting money from the initial campaign, but if you don’t address the problem and improve your inbox placement you are throwing good money after bad. Ensure that you are optimizing your email ROI — and making it accurately measurable — by reliably delivering your content to your subscribers. As a reputable sender, you should achieve high inbox placement with every campaign.

Knowing how many messages never reached the inbox is the first step in conducting any analysis of campaign performance. By monitoring your inbox placement rate, you will gain a solid view into how your email program is actually performing and a reliable basis from which to evaluate and optimize your email program.

source: http://www.targetmarketingmag.com/article/inbox-placement-rates-cant-measure-cant-see/