According to Validity’s 2024 State of Email report, roughly 1 in 6 legitimate marketing emails never reaches the primary inbox. For eCommerce brands sending at scale, that number translates directly into revenue that never had a chance to be earned, regardless of how good the subject line was.
When email performance starts declining, the instinct is to look at the email itself. The subject line wasn’t punchy enough. The offer wasn’t compelling. The send time was off. So the next campaign gets a new subject line, a stronger discount, a different send day. Performance stays flat or gets worse.
The problem with this loop is that it assumes the email is being seen. If a significant portion of your sends are landing in spam or the Promotions tab, no creative change will move the needle. You’re optimizing the message for an audience that never received it.
Deliverability problems and creative problems produce similar symptoms on the surface: lower open rates, lower click rates, flat or declining revenue from email. The difference is that one has a completely different root cause and a completely different fix. Here are the five signs that tell you which one you’re actually dealing with.
Sign 1: Your Open Rate Is Declining But Your Best Subscribers Still Engage
If your overall open rate is falling but the segment of subscribers who regularly open and click is holding steady, the problem is almost certainly not your subject line. What’s likely happening is that the engaged portion of your list is performing fine, while a growing unengaged segment drags down your aggregate numbers.
The more important question is what that unengaged segment is doing to your domain reputation at Gmail and Yahoo. Every send to subscribers who don’t open contributes a low-engagement signal to your sending domain. Over months of regular sending, that aggregate signal degrades your domain reputation, which causes Gmail to route more of your mail to Promotions or spam, including mail going to subscribers who would otherwise open it.
The tell: check your Google Postmaster Tools domain reputation. If it has moved from High to Medium, or if it has been sitting at Medium for an extended period, the engagement composition of your sends is likely the cause and a creative change will not fix it.
Sign 2: Your Delivery Rate Is High But Revenue From Email Has Been Quietly Falling
A 98% or 99% delivery rate is not evidence that your emails are reaching the inbox. Delivery rate measures whether the receiving mail server accepted your email. It says nothing about which folder it landed in.
A brand can have a 99% delivery rate and a 54% inbox placement rate simultaneously. The server accepted the mail. Gmail then routed nearly half of it to the Promotions tab or spam, where open and click rates are dramatically lower. Your ESP reports the 99% and calls it healthy. The 54% is invisible unless you’re measuring it separately.
This is the most common gap between what eCommerce brands think is happening and what is actually happening. If your delivery rate has been stable for months but email revenue has gradually declined, without a corresponding drop in list size or send frequency, inbox placement rate is the first thing to check, not subject line performance.
Sign 3: A/B Tests on Subject Lines Produce Inconsistent or Meaningless Results
Subject line A/B testing works well when the variable being tested is actually subject line performance. When a deliverability problem is present, the test results become noise.
If 35% of your sends are landing in spam and the remainder are split between inbox and Promotions, the open rates you’re measuring in your A/B test are drawn from a biased sample: only the people whose mail happened to land in the inbox. The winning subject line is not actually winning because it’s better copy. It’s winning because of variation in how many of its sends reached the inbox at all, which has nothing to do with the words in the subject line.
The practical sign: if you’re running consistent A/B tests and the winner changes frequently with no clear pattern, “free shipping” beats “exclusive offer” one week and loses the following week, deliverability variation is likely contaminating the test signal. The fix is not better test design. It’s getting placement stable before drawing conclusions from open rate data.
Sign 4: Open Rates Differ Significantly Between Gmail and Yahoo Subscribers
If your Gmail subscribers are opening at 18% while your Yahoo subscribers are at 9%, that is not a subject line problem. Different mailbox providers filter differently, maintain their own reputation signals, and apply different routing rules. A placement gap between providers is almost always a deliverability signal.
Yahoo responds to engagement signals faster than Gmail. A brand with a list quality problem will often see Yahoo inbox rates decline first, sometimes weeks before Gmail reputation moves. If you segment your open rate by email domain and Yahoo or Outlook is significantly underperforming Gmail, that gap is a deliverability warning that is easy to miss in aggregate reporting.
Similarly, if your engaged subscribers, those who opened in the last 30 days, are converting well but your broader list produces little response, the issue is not that your creative is failing the broader list. The issue is that the broader list is not receiving your emails in a visible location. Suppressing the unengaged segment and measuring placement separately is the diagnostic step, not another creative iteration.
Sign 5: Your ESP Metrics Look Fine But Revenue Keeps Falling
This is the most disorienting sign because everything in your dashboard appears healthy. Delivery rate is 99%. Bounce rate is below 0.5%. Unsubscribe rate is normal. Open rate is in line with industry benchmarks. And yet email-attributed revenue has been declining for two or three months.
The metrics your ESP shows you are real, but they are incomplete. None of them tell you what percentage of your sends reached the primary inbox. A brand with clean authentication, low bounce rates, and normal complaint rates can still have 40% of their Gmail sends going to the Promotions tab if their domain reputation has drifted to Medium over time. That 40% is generating near-zero opens and clicks, which flows directly into lower email revenue, and it is completely invisible in standard ESP reporting.
Google Postmaster Tools is the first place to look when this pattern appears. Check your domain reputation score and your spam rate. If domain reputation is Medium rather than High, that alone is enough to explain a meaningful reduction in primary inbox placement at Gmail. If complaint rate is trending upward in Postmaster Tools even though it looks fine in Klaviyo, that divergence indicates a measurement gap between what your ESP reports and what Gmail is actually seeing.
See where your emails are actually landing
Your ESP says delivered. InboxEagle shows you the inbox, Promotions, and spam split.
Inbox placement rate by provider, by campaign. The number your dashboard doesn't show you, and the one that explains why email revenue moves the way it does.
What to Do If You Recognise These Signs
The diagnostic path is the same regardless of which sign you identified.
First, check Google Postmaster Tools. Verify your domain reputation score (aim for High) and your spam rate (should be below 0.08% consistently). If either is off, you have confirmation that a deliverability problem exists. If both look fine, the issue may still be Promotions tab placement rather than spam, which Postmaster Tools does not surface directly.
Second, run inbox placement monitoring. This gives you the actual split: what percentage of sends to Gmail, Yahoo, and other providers are landing in inbox versus spam versus Promotions, per campaign. InboxEagle’s campaign-level placement monitoring runs against real mailboxes and returns results without requiring a manual seed list setup for each send.
Third, check your authentication. A DKIM pass rate below 100% in Postmaster Tools means at least one sending source is misconfigured. DMARC at p=none means you’re not enforcing. Either issue silently undermines the domain reputation you’re building with every send. The SPF, DKIM, and DMARC guide covers what to look for and how to fix each one.
Once you have placement data and authentication confirmed, the path forward is almost always the same: tighten your engaged segment, suppress non-openers beyond your threshold, and send three to four campaigns to your cleanest audience before expanding. Domain reputation responds to consistent clean sending. It does not respond to better subject lines.
If your program has already crossed into crisis territory, with an active blacklist listing or Postmaster Tools showing Low or Bad reputation, the email deliverability crisis recovery guide covers the step-by-step repair process.
The creative work matters. But it can only do its job when the emails are actually reaching the inbox.
Note: Content created with the help of AI and human-edited and fact-checked to avoid AI hallucinations.
