A customer writes that the shipping update never came. Klaviyo says delivered. The order email is not in their inbox, and your team is one resend away from making the complaint rate worse.
“Delivered” is the receiving server’s acceptance, and nothing more. That does not make the number useless: a delivery rate that drops is still a real signal, it just cannot show you the folder. It is not a promise that a person saw the message, and it is not a promise that the message reached the inbox. Delivery rate and inbox placement measure different steps. This page is the trace for the missing one: order confirmations, abandoned cart, welcome, and the campaign someone swears they never got.
If the ESP status is bounced or the send never left your account, that is email not delivering, not this problem.
Last verified: 26 September 2026.
Acceptance, placement, and a skip are three events
| ESP or SMTP status | What happened | What the customer experiences |
|---|---|---|
| 250 / Delivered | Receiving server accepted the message | Inbox, Promotions, Updates, spam, or a personal filter |
| 4xx deferral | Temporary refusal. The ESP may retry | Delay, then delivery or a later bounce |
5xx bounce, including 550 5.7.515 |
Permanent refusal | Nothing arrived. The ESP should not say delivered |
| Skipped, smart-sending, or suppressed | Your platform did not hand the message off | Nothing arrived, and there is no receiving-server record |
Gmail’s sender guidelines tell you how to authenticate and how they treat spam complaints. They do not define your ESP’s “delivered” column. Yahoo’s complaint rate is explicitly calculated on mail that was delivered to the inbox, which is a third number again: not attempts, and not every accepted message. When those three numbers get collapsed into one dashboard cell, “the customer didn’t get it” becomes unsolvable.
Why emails are delivered but not received
It is in spam. The usual reason a delivered campaign is “missing” for many customers at once. Start with why emails go to spam once you know the folder, not before.
It is in another Gmail category. Promotions and Updates are inboxes of a sort. They are not Primary, and shoppers who only watch Primary will open a ticket. A seed check that reports promotions is a placement result, not a delivery failure. Inbox, promotions, or spam is the distinction, and the Gmail troubleshooting guide covers whether a Promotions placement is actually a problem.
A mailbox rule or a corporate quarantine moved it. A forwarding rule, a “skip inbox” filter, or a company gateway can file or hold mail after the recipient’s MX has already accepted it. You will not see that in Klaviyo. You can sometimes see it in the customer’s headers if they find the message later.
The address you mailed is not the address they checked. Checkout typos, a plus-address, an old account, or a shared family inbox all produce a truthful “delivered” on a mailbox nobody is opening. Look at the profile before you resend.
Your own platform skipped it and the summary still looks healthy. Klaviyo Smart Sending, flow filters, and suppressions stop individual messages. A campaign overview can still show a high delivery rate because it is averaging everyone who was eligible. Open the profile. If the event says skipped, the customer is right that nothing arrived, and the fix is the rule, not the template.
Apple’s privacy feature confused the report. Mail Privacy Protection loads images and inflates opens. It does not remove mail. Do not treat a low open as proof the message vanished, or a high open as proof it was read by the customer who wrote in.
What to check on one missing email
- Search the exact address in the ESP. Read the event for that send: delivered, bounced, skipped, or suppressed, plus the timestamp.
- If the event is a bounce, copy the SMTP text.
550 5.7.515means Outlook.com rejected the From domain for failing high-volume authentication. Microsoft’s high-volume rule covers domains sending more than 5,000 messages a day to Outlook.com, Hotmail.com, and Live.com, enforced since May 5, 2025. The message was not delivered. Fix authentication using the Outlook rejection guide and send a new message. Resending the same failure repeats the bounce. - If the event is skipped, name the condition. Common ones on your store: Smart Sending because a flow and a campaign overlapped, a profile already in a flow, a suppression after a complaint, or a filter that required a placed order.
- If the event is delivered, ask the customer to search the mailbox for the from-name and the subject, including spam and Gmail tabs. Give them the from-address you actually used. A custom sending domain and a shared ESP domain look different in the inbox.
- If many people report the same template, stop treating it as a one-off. Check placement. InboxEagle seed mailboxes cover Gmail, Yahoo, AOL, and Outlook, with inbox, spam, and promotions as the outcomes. For Outlook authentication rejections, the bounce log is the evidence, because those are refused at SMTP time and never reach a folder.
What to check when a whole campaign “didn’t land”
Compare three counts for the same send:
- Recipients you intended to mail.
- Recipients the ESP actually attempted.
- Recipients the receiving servers accepted.
The gap between the first and the second is suppression, skips, and unsubscribes. The gap between the second and the third is bounces and deferrals. Neither gap is inbox placement. Placement is only visible with a seed mailbox or with the customer looking at the folder.
Then split by provider. A Gmail-only complaint wave with clean Yahoo delivery is a Gmail filtering problem. Use Postmaster Tools compliance status and spam rate, and the Gmail troubleshooting guide. A wave of Outlook bounces is authentication, not a spam folder. A wave across Gmail, Yahoo, AOL, and Outlook is the spam diagnosis.
Transactional mail and marketing mail disappear for different reasons. Order confirmations are often expected, so a miss becomes a support ticket within minutes. They also sometimes send from a different domain or a different provider than the campaign. Check the From domain on the missing message before you apply the campaign’s reputation story to a Shopify or SES receipt.
How to verify a missing email is fixed
- For a skip or suppression: the next event for that profile should be an attempted send, and the customer should be able to find that new message.
- For a bounce: the next attempt should not repeat the same SMTP code.
- For spam or a tab: a seed message at Gmail, Yahoo, AOL, or Outlook should show the folder you expect, on the same From domain and the same infrastructure as the real send.
- For a complaint-driven filter: watch the provider’s own complaint metric the next day. Gmail’s number is in Postmaster Tools. Yahoo’s is in Sender Hub. The ESP’s “delivered” percentage can stay at 99% the entire time and tell you nothing.
Do not verify by open rate. A privacy prefetch and a spam-folder open can both increment it.
What not to do when a customer says it never arrived
- Do not resend the full campaign to “make sure everyone got it.” You will mail the people who already received it, including the ones who complained.
- Do not add the customer’s address to a seed test and also to the live segment twice in an hour. That is how a support rescue becomes a complaint.
- Do not switch the from-name mid-thread. The customer is searching for the name on the original message.
When to escalate a delivered-but-missing email
Escalate to the ESP when the profile shows delivered, headers you can obtain show authentication failure, and the DNS you published is correct. The signing service and the DNS record disagree, and only the ESP can see the signed copy they transmitted.
Escalate to the mailbox provider’s postmaster process when you have a sustained rejection (Outlook 550 5.7.515 after SPF, DKIM, and DMARC pass on the messages you inspect) or a spam-rate problem you can document. Microsoft’s NDR article tells the sender to correct authentication. It does not offer a recipient-side switch that bypasses the check.
What to monitor so delivered means received
For your store, the messages that create “I never got it” tickets are order, shipping, password, welcome, and cart. Monitor those as their own streams if they use a different domain. Watch skip reasons on flows, bounce codes by provider, and inbox versus spam versus promotions at Gmail, Yahoo, AOL, and Outlook. What a deliverability dashboard should show is the longer list. Delivery rate alone is the metric that hides this problem.
InboxEagle
Find the folder the delivery report cannot see
A delivered status stops at the receiving server. InboxEagle shows whether that accepted mail landed in inbox, promotions, or spam at Gmail, Yahoo, AOL, and Outlook.
Sources
- Email sender guidelines, Google. Authentication and spam-rate requirements. These govern filtering after acceptance. They do not redefine ESP delivery counts.
- Postmaster Tools dashboards, Google. Spam rate is based on mail that reached an engaged inbox and was then marked spam.
- Sender best practices, Yahoo. Complaint rate is calculated on mail delivered to the inbox.
- Fix NDR 550 5.7.515, Microsoft. This rejection means the message was not accepted.