- Delivery means the server accepted your mail; deliverability means it reached the inbox, and only the second one matters.
- Fix things in order of impact: authentication, list quality, engagement, warmup, then content and infrastructure.
- Keep spam complaints under 0.1% (0.3% is Gmail's hard ceiling) and hard bounces under 2%.
- Verify imported or dormant lists before you send, and never mail a purchased list.
- Warm new domains and IPs over two to four weeks, starting with your most engaged subscribers.
- Watch Google Postmaster Tools, Microsoft SNDS, bounce logs and click trends together, not open rate alone.
Email deliverability is the share of your mail that reaches the inbox rather than the spam folder or a silent rejection. There is no single setting that fixes it. What works is a short list of fundamentals, applied in the right order and kept up over time.
This guide ranks those fundamentals by impact, gives you the numbers mailbox providers reward in 2026 and shows how to measure progress so you know whether a change actually helped.
Delivery vs deliverability
These two words get used interchangeably, and that confusion hides real problems.
- Delivery means the receiving server accepted the message. It did not bounce.
- Deliverability (or inbox placement) means the message landed in the inbox where the recipient will see it.
Your ESP dashboard usually reports delivery. A 99% delivery rate can still mean a quarter of your mail sits in spam, because accepted mail is routed after acceptance based on reputation, authentication and engagement. The goal of everything below is to push accepted mail into the inbox.
The five pillars of inbox placement
Mailbox providers weigh five groups of signals on every send. Weakness in one drags down the others.
| Pillar | What providers look for | Where to check |
|---|---|---|
| Authentication | SPF, DKIM and DMARC passing and aligned | DMARC Checker, SPF Checker |
| Reputation | Domain and IP history at each provider | Postmaster Tools, SNDS, Sender Reputation Checker |
| List quality | Opted-in, valid addresses; fast suppression | Bounce and complaint logs |
| Engagement | Opens, clicks, replies, move to inbox | ESP reporting, trend over time |
| Infrastructure | Matching reverse DNS, clean IPs, no listings | Reverse DNS Checker, Blacklist Checker |
Reputation is the pillar that ties the rest together: it is each provider’s running judgment of the other four. If you want the mechanics behind it, start with what sender reputation is.
The playbook, in priority order
Work through these steps from top to bottom. The first two prevent most spam-folder problems outright.
1. Authenticate every message
Publish one SPF record, sign all mail with DKIM on your own domain and publish DMARC, starting at p=none and moving toward quarantine or reject. Make sure the From domain aligns with the domain that passes SPF or DKIM. Every tool that sends as you (CRM, helpdesk, billing) needs the same treatment. The email authentication guide walks through each record.
2. Mail only people who opted in, and keep the list clean
Permission is the foundation. Use confirmed opt-in where you can: it guarantees the address works and the person meant to subscribe. The double opt-in guide covers the trade-offs.
Then keep the list clean:
- Suppress hard bounces after the first failure.
- Suppress anyone who complains, immediately and permanently.
- Run a re-engagement series for subscribers inactive six to twelve months, then remove non-responders.
- Verify any imported, old or dormant list before it touches a campaign.
For verification, dedicated services such as ZeroBounce and NeverBounce are the specialists, and all-in-one platforms such as SendPulse include a built-in verifier that handles routine list hygiene without exporting your data. Our verification tools comparison ranks the options.
3. Earn engagement with relevant, segmented mail
Opens, clicks and replies are the strongest positive signals you can generate. Segment by activity (recent openers vs dormant), interest and lifecycle stage. Send your best content to your most engaged readers first, which banks positive signals before the broader send goes out. Timing also helps; see the send-time optimization guide.
4. Warm up new domains and IPs gradually
A new domain or IP has no history. A sudden large send from it looks exactly like a spammer who just registered a domain. Ramp up over two to four weeks, as described below.
5. Tidy content and infrastructure
- Write subject lines that match the content.
- Include a plain-text part alongside HTML.
- Keep images balanced with real text; avoid image-only emails.
- Do not use public link shorteners. Use a branded tracking domain.
- Support one-click unsubscribe with
List-UnsubscribeandList-Unsubscribe-Postheaders. - Make sure each sending IP has a PTR record that matches its forward DNS. Check it with the Reverse DNS Checker.
Choosing a sending platform that helps, not hurts
Your ESP controls a lot of your deliverability: the quality of its shared IP pools, how fast it processes bounces and complaints, whether it lets you set up custom DKIM and Return-Path, and how good its warmup tooling is.
When comparing platforms, look for:
- Custom domain authentication (SPF include, DKIM on your domain, custom Return-Path).
- Automatic bounce and complaint suppression.
- Shared pools that are actively policed, plus a dedicated IP option when your volume grows.
- Built-in list verification or easy integration with a verifier.
- Clear reporting by mailbox provider, not just an overall number.
Reputable options include Brevo, Mailchimp, SendPulse and Amazon SES, each with different strengths on price, automation and control. Some bundle an SMTP service with a dedicated IP on higher tiers, while SES is cheaper at scale but leaves more of the setup and monitoring to you. Our bulk email services comparison goes deeper.
A dedicated IP makes sense only once you send steady, high volume. Below that, you do not produce enough signal to keep its reputation stable. The shared vs dedicated IP guide helps you decide.
Separate your mail streams
If you send both transactional mail (receipts, password resets, alerts) and marketing mail (newsletters, promotions), keep them apart. They behave very differently. Transactional messages are expected and get opened quickly. Marketing messages vary in engagement and draw more complaints.
When both share one domain and IP, a poorly received campaign can push your order confirmations into spam. A common setup is:
- Marketing from a subdomain such as
news.example.com, through your marketing platform. - Transactional mail from another subdomain such as
mail.example.comornotify.example.com, through an SMTP or API service. - Separate IP pools where your provider supports it.
Each stream then builds its own reputation, and problems in one do not leak into the other. The transactional vs marketing deliverability guide covers the setup in detail.
Treat each mailbox provider on its own terms
The big providers share principles but differ in emphasis, so segment your reporting by provider and adjust.
Gmail
Gmail leans heavily on engagement and domain reputation. It will sort promotional mail into the Promotions tab, which is not the same as spam and is not a deliverability failure in itself. Watch the spam rate and domain reputation in Postmaster Tools, and pay attention to 4.7.28 rate limit deferrals, which usually mean you are sending faster than your reputation supports.
Microsoft (Outlook, Hotmail, Live)
Microsoft weighs IP reputation and consistency. New IPs get throttled aggressively, and blocks often show up as 550 5.7.1 errors with an internal reference code. Register in SNDS and the Junk Mail Reporting Program, and ramp volume slowly on new infrastructure.
Yahoo and AOL
Yahoo applies the same bulk sender rules as Gmail and pays close attention to complaints. Sign up for its Complaint Feedback Loop so reports flow back to you. Deferrals with codes such as 421 are Yahoo’s way of saying slow down.
Corporate filters
B2B mail often passes through Microsoft 365, Proofpoint, Mimecast or Barracuda. These rely more on blocklists and IP reputation, and some quarantine mail before the recipient ever sees it. Clean authentication, a proper PTR record and a clean blocklist record matter most here.
How to warm up a new domain or IP
Warmup means increasing volume in steps so each provider learns that your mail is wanted. Start with your most engaged recipients, because their positive reactions build trust fastest. Treat the schedule below as a ceiling: if bounces or complaints rise, hold at the current level until they settle.
| Stage | Approximate daily volume | Audience |
|---|---|---|
| Days 1 to 2 | 50 to 500 | Most engaged subscribers only |
| Days 3 to 5 | Around 1,000 | Recent openers and clickers |
| Days 6 to 9 | Around 5,000 | Broaden slightly, watch bounces |
| Days 10 to 14 | 10,000 to 25,000 | Wider audience, watch for throttling |
| Days 15 to 21 | Up to 50,000 | Near full volume if metrics hold |
| Week 4 onward | Full volume | Keep a steady cadence |
Temporary deferrals such as 421 or 4.7.28 during warmup are normal throttling signals. Slow down; do not push harder. Our warmup guide has provider-specific tips.
The numbers that define healthy sending in 2026
Providers publish some limits outright. Crossing them gets you filtered or rejected.
- Spam complaints under 0.1%. That is one complaint per 1,000 delivered. Gmail filters heavily above 0.3%.
- Hard bounces under 2%. Higher rates point to stale or unverified data.
- Full authentication for bulk senders. Since February 2024 at Gmail and Yahoo, and May 2025 at Outlook, senders above roughly 5,000 messages a day must pass SPF and DKIM, publish DMARC with alignment and offer one-click unsubscribe.
- Unsubscribes honored within two days. A Gmail and Yahoo requirement.
- Matching reverse DNS. Every sending IP needs a PTR record that resolves back.
- Steady volume. A tenfold jump overnight reads like a compromised account.
For context on how your numbers compare to others in your sector, see our deliverability benchmarks by industry.
Signals that help and signals that hurt
| Factor | Helps | Hurts |
|---|---|---|
| Permission | Confirmed opt-in | Purchased, scraped or appended lists |
| Authentication | SPF, DKIM, DMARC aligned and passing | Missing, broken or unaligned records |
| List hygiene | Bounces and complainers removed immediately | Repeated sends to dead or inactive addresses |
| Engagement | Opens, clicks, replies, move to inbox | Deletes without reading, spam reports |
| Volume | Predictable schedule | Spikes, or long silence then a blast |
| Infrastructure | Matching PTR, clean IP, no listings | Missing rDNS, listed IPs |
| Unsubscribe | One-click, processed fast | Hidden link, login required, slow |
How to measure deliverability
Track four things and read them together.
Inbox placement
Use seed testing or panel data to estimate what share of accepted mail reaches the inbox. Aim for 90% or better. Industry averages sit in the mid 80s, and anything below about 70% needs urgent work.
Bounce rate
Keep hard bounces under 2% and look at the codes, not just the totals. A rise in 5.1.1 means list decay. A rise in 5.7.1 or 554 usually means a policy or reputation block. The bounce rate guide explains how to read them.
Complaint rate
Read it from Google Postmaster Tools, Yahoo’s Complaint Feedback Loop and Microsoft’s JMRP. Your ESP should also process these automatically.
Engagement trends
Treat opens as a trend, since Apple Mail Privacy Protection inflates them. Give clicks and replies more weight. A stable delivery rate with falling clicks often means mail is drifting into spam.
Why your emails are going to spam, and what to check first
If mail that used to land now goes to spam, something measurable changed. Work through these in order.
- Broken authentication. A DNS edit, a new tool or an expired DKIM key can break alignment overnight. Run the Sender Reputation Checker.
- A complaint spike. One irrelevant or unexpected campaign can push you past the threshold. Pull back to engaged recipients.
- A bad import. Old or unconsented addresses raise bounces and trap hits together. Remove the segment.
- A new blocklisting. Scan with the Blacklist Checker and follow the blacklist removal guide.
- A volume spike or gap. Return to a steady cadence and re-warm if you have been quiet for weeks.
- Slipping engagement. Prune inactive subscribers and sharpen segmentation. The sunset policy guide shows how.
For a longer checklist of causes, read why emails go to spam.
A pre-send checklist for every campaign
Most deliverability incidents start with one campaign that should not have gone out as it did. A two-minute check before each send catches the usual problems.
- Audience. Is this segment made of people who opted in and engaged recently? Exclude anyone inactive for six months or more unless this is a deliberate re-engagement send.
- Source. Does the list include a new import, event list or partner list? If so, has it been verified?
- Volume. Is this send much larger than your usual volume? If it is more than two or three times your normal size, split it over several days.
- Authentication. Has anything changed in DNS or in your sending tools since the last campaign? If so, send a test to a Gmail account and check the headers show
spf=pass,dkim=passanddmarc=passwith the Header Analyzer. - Links. Are all links on your own or reputable domains, with no public shorteners? Do they all work?
- Unsubscribe. Is the unsubscribe link visible, and is the one-click header present?
- Expectations. Does the subject line match the content, and does the sender name match what subscribers signed up for?
If any answer is “no” or “not sure,” fix it before you hit send. Recovering from a bad campaign takes far longer than preventing one.
A monthly deliverability routine
Deliverability is maintenance, not a project. A light monthly routine catches most problems early:
- Check Postmaster Tools domain reputation and spam rate.
- Scan domains and IPs for blocklist listings.
- Review hard bounce and complaint rates by campaign.
- Confirm SPF, DKIM and DMARC still pass after any DNS or tool change.
- Read a week of DMARC aggregate reports for unknown senders.
- Move inactive subscribers into your re-engagement flow.
Done consistently, this takes an hour a month and saves you from the weeks it takes to repair a damaged reputation.
Frequently asked questions
What is the fastest way to improve email deliverability?
Fix authentication and stop mailing people who do not engage. Check SPF, DKIM and DMARC with our Sender Reputation Checker, then send your next few campaigns only to subscribers who opened or clicked in the last 90 days. Those two moves resolve most sudden spam-folder problems within a couple of weeks.
What is a good inbox placement rate?
Around 90% or higher is strong. Industry averages usually land in the mid 80s, meaning roughly one in six messages misses the inbox. Below about 70% you have a real problem worth investigating right away. Measure placement with seed tests or panel data, because your ESP's delivery rate only tells you what was accepted.
Does a dedicated IP improve deliverability?
Only if you send enough steady volume to build and maintain its reputation, typically hundreds of thousands of messages a month. Below that, a well-managed shared pool usually performs better because it already has history. A dedicated IP gives you control but also full responsibility for every mistake.
Why are my emails going to spam when they used to reach the inbox?
Something changed. The usual suspects are a broken DNS record, a new sending tool that is not authenticated, a complaint spike from one campaign, a bad list import, a new blocklisting or a volume jump. Check authentication first, then your blocklist status, then your recent sends.
Do spam trigger words still matter?
Much less than they used to. Modern filters rely on reputation and engagement far more than individual words. That said, misleading subject lines, all-caps shouting, image-only emails and link shorteners still hurt, mostly because recipients react badly to them and complain.
How often should I clean my email list?
Suppress hard bounces and complaints automatically after every send. Run a re-engagement pass on subscribers inactive for six to twelve months at least twice a year, and verify any list that has been dormant for more than a few months or came from an import before you mail it.