Email shows Delivered in Resend but the recipient never got it

Symptom: the Resend dashboard and webhooks show delivered, but the recipient insists nothing arrived.

1. Confirm the cause: in Resend, Delivered is set once the recipient server accepts the email with a 250 OK response. What happens next (inbox, spam, queue, discard) is decided by the inbox provider, corporate filters, or the user's own rules, and providers do not share how they filter afterward.
2. If you can reach the recipient, ask them to check: corporate spam filters or firewalls, personal inbox filtering rules, promotional/spam/deleted folders, and group inboxes or queues. If they find it, have them mark it Not Spam or allowlist your sending domain.
3. If you cannot reach the recipient, improve your odds for next time: configure DMARC to build trust with the provider, warm up new domains slowly before large volumes, make all links use your own sender domain, turn off open and click tracking, reduce images, and keep wording succinct and non-spammy.
4. Note the distinction from a bounce: a bounce means the server rejected it and Resend tells you why. Delivered-then-missing is a downstream filtering decision with no signal back.
5. Verify: ask the recipient to search all folders including spam for your sender address, and check whether corporate quarantine held it.

Documented in Resend knowledge base: Delivered is marked on the recipient server's 250 OK acceptance; the server may then inbox, queue, spam-folder, or discard; providers share no info on later filtering; recipient should check spam/filters/quarantine and mark Not Spam or allowlist; sender-side improvements include DMARC, warm-up, own-domain links, tracking off, fewer images. Evidence: resend.com/docs/knowledge-base/what-if-an-email-says-delivered-but-the-recipient-has-not-received-it.