Last verified: July 31, 2026.
When legitimate marketing or operational email lands in spam, the right response is diagnosis—not a promise that one change will “fix” inbox placement. Delivery, acceptance, inbox placement, and engagement are different signals. A message can be accepted by a receiving server and still be filtered away from the primary inbox.
Start with identity and consent
Inventory every domain and provider that sends mail on your behalf. Check that SPF authorizes the right sending services, that DKIM signing is active, and that DMARC is published with alignment understood before you move to a stricter policy. Google’s sender guidelines identify authentication, low unwanted-mail rates, and easy unsubscribe as core requirements for high-volume senders; Yahoo likewise documents SPF, DKIM, DMARC, and separating marketing traffic from transactional mail.
Then review the acquisition path. A clean technical setup cannot compensate for messages sent to people who did not expect them. Use clear consent, make opt-out easy, and suppress hard bounces, complaints, and disengaged recipients according to your own retention and compliance policies.
Measure before changing volume
Break reporting down by sending domain, stream (marketing versus transactional), mailbox provider, and campaign. Compare delivery errors, complaint signals, bounce patterns, authentication results, and engagement trends. A small, well-defined segment is safer for testing than a sudden volume increase. If a change affects one provider but not another, preserve that detail: it is more useful than a blended open-rate number.
What to do next
Document the baseline, correct authentication and list-quality problems, and retest with controlled sends. For an overview of the technical and operational services DeliverabilityAgent provides, see Why DA. If you need to discuss a custom email infrastructure review, contact DeliverabilityAgent. This guide is educational; mailbox providers make the final filtering decisions.
For primary requirements, consult Google’s Email sender guidelines and Yahoo Sender Best Practices.
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For choosing a tool or service after the diagnostic work, use our email deliverability software evaluation framework.