Delivered is not the same as seen
Email platforms report a 'delivered' figure that looks reassuringly high. It only means the receiving server accepted the message. Whether that message landed in the primary inbox, a promotions tab or the spam folder is a separate question, and it is the question that matters.
So treat deliverability as three distinct outcomes. Delivery: the server accepted the mail. Placement: where it landed. Attention: whether anyone engaged. Most teams measure the first, guess at the second and blame the copy for the third.
How mailbox providers decide
Gmail, Outlook, Yahoo, Apple and corporate filters each use their own systems, and none publishes the full recipe. But the principles are consistent. They ask: can we verify who sent this, do we trust that sender based on history, and do our users seem to want it?
Fig. 01 · Stack
Tap to explore
What sits under inbox placement
Content
Links, images, formatting and wording; rarely the root cause on its own
Engagement
Opens, replies, moves to inbox, deletes without reading, complaints
List quality
Valid, consented, recently engaged addresses; no traps or purchased data
Reputation
Domain and IP history built over months of sending behaviour
Authentication
SPF, DKIM and DMARC proving you are who you claim to be
Authentication comes first because it is binary: either the receiving server can verify you or it cannot. Our explainer on SPF, DKIM and DMARC walks through the setup. Major providers now expect authentication from anyone sending in volume, so this is the price of entry, not an advantage.
Reputation is earned slowly and lost quickly. It attaches increasingly to your sending domain rather than only to an IP address, which means that changing email platforms does not reset a bad reputation.
Engagement is the signal that matters most
Mailbox providers watch what their users do with your mail. Opening, replying, adding you to contacts and dragging messages out of spam all help. Deleting unread, ignoring for months and pressing 'report spam' all hurt. The complaint is the loudest negative signal you can receive.
This is why list hygiene and deliverability are the same subject. Every unengaged address you keep mailing is a small vote against you. Sending to fewer, more interested people often increases total inbox placement and total revenue at the same time.
Calculator
Complaint and bounce rates for one send
Calculate the two numbers to watch after every campaign. Compare against your own history and the current guidance published by the major mailbox providers.
Hard bounce rate
0.5%
A spike usually means an old or poorly sourced segment was mailed.
= bounced / sent
Complaint rate on delivered mail
0%
Mailbox providers publish guidance on acceptable levels; check their current documentation.
= complaints / (sent - bounced)
Defaults are illustrations. Use your own numbers. Nothing you enter leaves this page.
The list quality rules worth enforcing
- Never buy, rent or scrape lists. They contain people who did not opt in and often contain spam traps designed to catch exactly this behaviour.
- Confirm risky signups. Double opt-in, or a confirmation step for sources prone to typos and bots, keeps bad addresses out at the door.
- Remove hard bounces immediately. Most platforms do this automatically; check that yours does.
- Sunset the unengaged. Decide a period of inactivity, run a re-permission sequence, and stop mailing those who do not respond.
- Make leaving easy. A visible unsubscribe link and one-click unsubscribe headers turn would-be complainers into quiet leavers.
The last point is counter-intuitive for many marketers. Hiding the unsubscribe link does not keep people on the list. It pushes them to the spam button, which damages your ability to reach everyone else. See CRM data hygiene for the broader routine.
Warming up a new domain or IP
A brand-new sending domain or dedicated IP has no history, and providers are cautious with strangers. Warming up means starting with small volumes sent to your most engaged recipients and increasing gradually as positive signals accumulate.
The exact schedule depends on your volume and platform, so follow your email service provider's current warm-up guidance. The principle never changes: send your best mail to your best people first, and let the reputation build before you mail colder segments.
The reputation loop
Fig. 02 · Cycle
Tap to explore
How reputation compounds, in both directions
Relevant mail to engaged people
Diagnosing a deliverability drop
When clicks or revenue fall suddenly, resist the urge to rewrite subject lines. Work through the layers from the bottom. Has anything changed in authentication, such as a new tool sending on your behalf without being added to SPF or DKIM? Did you mail an old segment? Has complaint volume risen?
Self-diagnostic
0/5Deliverability triage
Run through this when performance drops without an obvious reason.
01Do SPF, DKIM and DMARC all pass for your most recent campaigns?
If yes: Authentication is not the cause. Move to list and engagement checks. If no: Fix authentication first. Check whether a new sending tool was added recently.02Did you mail a segment that has not been mailed in a long time?
If yes: That is a likely cause. Re-permission or suppress that segment and send only to engaged recipients for a while. If no: Look at complaint and bounce trends next.03Have complaints or bounces risen over the last few sends?
If yes: Tighten targeting to recent engagers and review signup sources for bad data. If no: Check provider-specific data; the problem may sit with one mailbox provider.04Does one mailbox provider show worse results than others?
If yes: Use that provider's postmaster tools and documentation to see its view of your domain. If no: Consider content and offer fatigue as contributing factors.05Did your sending volume jump suddenly?
If yes: Sudden spikes look suspicious. Ramp volume more gradually. If no: Review recent changes to templates, links and tracking domains.
Who owns deliverability?
In many organisations nobody does. The marketing team sends, IT manages DNS, a vendor runs the platform and the store sends its own receipts. When placement drops, each assumes another is responsible. Name one owner who can see authentication results, complaint and bounce trends and provider postmaster data, and who has the authority to pause a send or suppress a segment.
That owner should also sit in the room when new tools are bought. Every new platform that sends email in your name, from event software to invoicing, is a potential deliverability and authentication risk. A simple rule, that no tool sends as your domain until it is authenticated and approved, prevents most surprises.
Deliverability across markets
Mailbox provider mix varies by country and by audience. A consumer list in one market may be dominated by a single webmail provider; a B2B list may be mostly corporate servers with their own filtering appliances. Look at your list by receiving domain to understand who you really need to satisfy, and use the tools and documentation of the providers that matter most to you.
Where content does matter
Content is rarely the root cause, but it is not irrelevant. Broken HTML, link shorteners with poor reputations, a single giant image with no text, and misleading subject lines can all count against you. Write as you would to a person: clear sender name, honest subject, real text, working links. Our guides on email design and subject lines cover the craft.
The spam folder is not a punishment for bad copy; it is the receipt for mailing people who stopped caring.
Key takeaways
- 01Delivery, inbox placement and attention are different outcomes; measure them separately.
- 02Authentication is now the entry fee for bulk sending, not a competitive edge.
- 03Engagement and complaints are the signals mailbox providers weigh most heavily.
- 04Sending to fewer, more engaged people often improves both placement and revenue.
- 05When performance drops, diagnose from authentication upwards before touching the copy.
Frequently asked
- What is a good email deliverability rate?
- The delivered rate your platform shows is usually high and says little about inbox placement. Focus instead on low and stable bounce and complaint rates, healthy engagement among recent subscribers, and the reputation data in mailbox providers' postmaster tools. Compare against your own history and current provider guidance rather than generic benchmarks.
- Why are my emails going to spam?
- The usual causes are failed or missing authentication, mailing people who have not engaged for a long time, rising complaints, poorly sourced or purchased addresses, and sudden spikes in volume. Content problems contribute less often. Work through these layers in order before rewriting copy.
- Does changing email platform fix deliverability?
- Rarely. Reputation increasingly attaches to your sending domain, so a new platform with the same domain and the same list behaviour will inherit the same problems. Fix list quality, authentication and targeting first; switch platforms for other reasons.
- What is email warm-up?
- Warm-up is the gradual increase in sending volume from a new domain or IP so mailbox providers can learn to trust it. You start with small sends to your most engaged recipients and scale up as positive signals build. Follow your provider's current warm-up guidance for the schedule.
- Does double opt-in improve deliverability?
- It usually improves list quality, because it filters out typos, bots and people who did not really mean to subscribe. Better list quality supports better reputation. The trade-off is fewer total signups, which is often worth it for sources prone to bad data.
Published by Fabulous.Media, a network of specialist marketing agencies. Updated 9 October 2026. Platform features change often; check current official documentation before acting on platform-specific detail.
