To improve email deliverability, publish SPF, DKIM and DMARC records, mail only people who opted in and still read your mail, and keep your Gmail spam rate under 0.1%. After that, grow volume slowly and check Google Postmaster Tools every Monday.
Most deliverability problems stay hidden. Your platform says delivered, the open rate slips a little each month, and nobody notices that more of the list now sees you in spam.
The rules got stricter in 2024. Gmail and Yahoo began enforcing sender requirements that February, and Microsoft followed for Outlook.com on May 5, 2025. Since November 2025, Gmail has been ramping up enforcement, and failing mail can now get a temporary or permanent rejection. A setup that passed in 2023 can fail without warning today.
On this page
- What is email deliverability?
- Why are your emails going to spam?
- SPF and DKIM in plain language
- How DMARC alignment and reports work
- Gmail sender requirements compared with Yahoo and Outlook
- What the 0.1% and 0.3% spam limits mean for your sends
- List hygiene that protects your sender reputation
- How much to send, and how fast to grow it
- Content habits that keep readers from reporting you
- How to check your sender reputation
- How to improve email deliverability in 30 days
What is email deliverability?
Email deliverability is the share of your mail that reaches the inbox instead of the spam folder or a bounce. Senders measure it as inbox placement, the percentage of delivered mail that lands in the inbox. That differs from the delivery rate your platform shows, which counts every message a server accepted, wherever it went next.
The gap between the two can be wide. Say a newsletter goes to 10,000 people and the platform reports 98% delivered. If a fifth of those 9,800 messages land in spam, only 7,840 reach an inbox. The report still looks healthy.
Why are your emails going to spam?
When your emails are going to spam, check five causes in this order: authentication, complaints, list quality, volume and content.
| Cause | What you see | Where to look first |
|---|---|---|
| Failed authentication | Bounces with error 550 5.7.515 from Outlook.com, or Gmail rejections | Postmaster Tools compliance status and your DMARC reports |
| Spam complaints | Gmail spam rate above 0.1% | Postmaster Tools spam rate dashboard |
| Old or bought addresses | Hard bounces and blocklist listings | Your platform's bounce report |
| Volume spike | Delays and deferrals after one big send | Your platform's delivery log |
| Misleading content | Spam reports within hours of a send | Subject lines, From name and link domains |
The order matters. A clean list can't help mail that Gmail turns away at the door, and good copy won't outweigh a 0.4% complaint rate.
SPF and DKIM in plain language
SPF, DKIM and DMARC are three DNS records that prove your email comes from you. Without them, a receiving server can't tell your newsletter from a forgery sent in your name.
SPF is your approved sender list. It's a TXT record that names every service allowed to send as your domain. That covers your newsletter platform, the CRM your sales team works from, your help desk and your office mail. The SPF standard, RFC 7208, sets two limits that people break by accident.
A domain gets one SPF record, and a second one makes the check fail with a permanent error. One check may trigger no more than 10 DNS lookups. Each include entry for a new tool counts toward that limit, which is how a domain that passed last year starts failing after three or four new software subscriptions.
DKIM works like a tamper seal. Your sending platform signs each message with a private key, and you publish the matching public key in DNS. If the message changes in transit or the keys don't match, DKIM fails. Sign with your own domain instead of the platform's shared one, because DMARC alignment depends on it.
How DMARC alignment and reports work
DMARC checks that the domain in your From address, the one readers see, matches a domain that passed SPF or DKIM. Mail admins call that match alignment. Your DMARC record then tells receivers what to do with mail that fails. A policy of p=none means monitor and report, p=quarantine means treat it as suspicious, and p=reject means refuse it.
The reports matter more than the policy at the start. Add a rua address to the record, as Yahoo strongly recommends. Receivers then send you daily summaries of every source using your domain, including senders nobody remembered, such as an n8n automation workflow that emails alerts.
Take a clinic that sends reminders from its booking software and a newsletter from a separate platform. Both belong in one SPF record, and both need DKIM with the clinic's domain. Miss the booking tool and its reminders fail DMARC while the newsletter passes.
Gmail, Yahoo and Microsoft all accept p=none today, so you don't need a stricter policy to comply. Quarantine and reject stop strangers from sending fake mail in your name, and Microsoft recommends p=reject. Move up only when your reports show every real sender passing. Under p=reject, a forgotten invoicing tool means your own invoices get refused.
Gmail sender requirements compared with Yahoo and Outlook
Gmail sender requirements come in two tiers. Every sender has to pass SPF or DKIM and keep the spam rate below 0.3%. Gmail wants valid forward and reverse DNS (PTR) records, a TLS connection and messages formatted to RFC 5322 as well. Bulk senders, which Google defines as anyone sending close to 5,000 or more messages a day to personal Gmail accounts, carry extra duties.
Gmail's email sender guidelines, Yahoo's sender best practices and Microsoft's Outlook.com policy line up closely for bulk mail, with a few gaps.
| Rule | Gmail | Yahoo | Outlook.com |
|---|---|---|---|
| Who counts as bulk | Close to 5,000+ messages a day to personal accounts | No number published | 5,000+ messages a day |
| Authentication | SPF, DKIM, DMARC | SPF, DKIM, DMARC, and DMARC must pass | SPF, DKIM, DMARC, with SPF and DKIM both passing |
| Minimum DMARC policy | p=none, aligned with SPF or DKIM | p=none, relaxed alignment accepted | p=none, with p=reject recommended |
| Spam rate | Below 0.3%, target under 0.1% | Below 0.3% | No public number |
| Unsubscribe | One-click header plus a visible link in the body | One-click header, honored within 2 days | Clearly documented and findable |
| Enforced since | February 2024, stricter from November 2025 | February 2024 | May 5, 2025 |
| Failing mail | Temporary or permanent rejection | Spam folder or rejection | Junk folder, then rejection |
Two details catch small businesses out. Gmail's bulk sender status has no expiry date, so one big holiday campaign can make you a bulk sender for good. And one-click unsubscribe means two headers, List-Unsubscribe and List-Unsubscribe-Post, so check that your platform adds both.
Microsoft's postmaster policy sends failing bulk mail to junk first, and Microsoft may reject it if the problem stays. The bounce then carries error 550 5.7.515. Microsoft's fix for error 550 5.7.515 lists the header checks to run, so start with your DNS records.
What the 0.1% and 0.3% spam limits mean for your sends
Your spam complaint rate is the share of delivered mail that readers mark as spam. Google asks senders to stay below 0.1% and never reach 0.3%. Since June 2024, Gmail bulk senders above 0.3% can't get mitigation help. They regain it only after 7 straight days below that line.
Put numbers on it. A send to 20,000 people that collects 60 spam reports sits at 0.3%, and at 0.1% your limit is 20 reports. Google and Yahoo both measure against mail that reached the inbox, so treat this as a rough guide, but the scale holds: a few dozen annoyed readers can move you from safe to at risk.
The fastest way to cut complaints is to make leaving easier than reporting. A reader who can't find the unsubscribe link presses "Report spam" instead, and that report counts against you.
List hygiene that protects your sender reputation
List hygiene means mailing only people who asked for your email and still want it. Old, bought and unconfirmed addresses raise both bounces and complaints, and providers weigh both when they place your mail.
Google's guidelines say it plainly. Don't buy addresses from other companies, and confirm each address before you subscribe it. It even suggests unsubscribing people who don't open or read your messages. Remove hard bounces after the first failure, and set a sunset rule for everyone else, such as no opens or clicks in six months.
Blocklist operators plant spam traps to catch careless senders. Spamhaus describes several kinds of spamtraps:
- Pristine traps were never given to a real person or shown on a website. Only scraped or bought data reaches them.
- Typo domain traps sit on lookalike domains and collect addresses mistyped into sign-up forms.
- Old mailboxes an ISP turned off, and expired domains a trap owner bought, become dead address and dead domain traps. Hitting one means you kept mailing long after the person left.
Spamhaus says confirmed opt-in at the point of collection is a perfect way to keep typo traps off your list. You lose some sign-ups who never click the confirmation link, and those are the addresses you least want.
How much to send, and how fast to grow it
Steady volume builds trust with mailbox providers, and sudden jumps erode it. Google tells senders to start with a low volume to engaged users and raise it slowly. It warns against spikes, such as doubling your volume overnight, and asks for a consistent rate instead of bursts.
Volume matters most for email deliverability when something changes: a new domain, platform or dedicated IP, or a list that grew fast. Each one weakens the history providers judge you on. The fix is a warm-up. Mail recent openers and clickers first, then widen the audience in stages while bounces and complaints stay flat.
A business moving 30,000 subscribers to a new platform shouldn't mail all of them on day one. Start with the 3,000 most engaged readers and check the next day's bounces and Postmaster Tools. Then add more of the list with each send over the following weeks. Slow feels wasteful in week one, but it costs far less than rebuilding a damaged reputation.
Keep mail types apart, too. Google advises against mixing content, such as a promotion inside a receipt, and wants one From address per category of mail. Send invoices, password resets and the reminders that help you reduce cart abandonment from their own address, or better, their own subdomain. A weak campaign then can't drag down the mail customers wait for.
Content habits that keep readers from reporting you
Content affects email deliverability through your readers, because their reactions feed your reputation. Google's content rules are about transparency, and they contain no list of banned words. Links in the body should be visible and clear, and nothing should hide behind HTML or CSS tricks.
These habits are our own advice, and each one avoids anything that looks like a disguise:
- Use a From name your subscribers recognize, and keep it the same from send to send.
- Write subject lines that describe the email. A subject that promises a sale the body doesn't deliver earns spam reports.
- Skip link shorteners, since they hide the destination.
- Pair images with real text and add a plain-text version. An email that is one large image shows a blank box to anyone who blocks images.
- Give a reply-to address that a person reads.
A software company that titles a product update "Your account needs attention" will get its opens. It will also get spam reports from every customer who feels tricked, and those reports outlast the open rate.
How to check your sender reputation
Check your sender reputation with the tools mailbox providers publish: Google Postmaster Tools for Gmail and Microsoft SNDS for Outlook.com. DMARC reports and your platform's bounce figures fill in the rest.
Start with Postmaster Tools. Verify your domain, then read these Postmaster Tools dashboards first:
- Compliance status shows whether your mail meets Gmail's sender rules. Data updates within about 24 hours, but Google says a fixed requirement can take up to 7 days to show.
- Spam rate covers your DKIM-authenticated mail that readers marked as spam after it reached the inbox. Hold it below 0.1%.
- The Authentication dashboard gives your pass rate for each of the three checks.
- Delivery errors counts the authenticated mail Gmail rejected, as a percent of the total.
Don't build reports around the Domain and IP Reputation dashboards. Google says it will retire both with the old Postmaster Tools interface. On low-volume days Google may leave data out, so small senders should read trends across weeks.
For Outlook.com, sign in to Microsoft's Smart Network Data Services (SNDS) with a Microsoft account. Then request access to the IPs you're responsible for. Access expires 10 months after approval, so put the renewal in your calendar. On a shared IP, other senders' habits affect your email deliverability too, so ask your platform for its numbers.
How to improve email deliverability in 30 days
Fix authentication first, then the list, then monitoring. Weeks 1 and 3 need someone with access to your domain's DNS settings, so find that login before you start.
- Week 1: list every tool that sends as your domain. Publish one SPF record within the 10-lookup limit, turn on DKIM in each tool, and publish DMARC at p=none with a rua address.
- Week 2: remove hard bounces and suppress contacts with no opens or clicks in six months. Add confirmed opt-in to sign-up forms, then test both unsubscribe methods.
- Week 3: verify your domain in Postmaster Tools, register dedicated IPs with SNDS, and read your first DMARC reports. Add any sender you missed to SPF and DKIM.
- Week 4: move receipts and account mail to their own address or subdomain. Start a Monday check of spam rate, authentication, bounces and new DMARC sources.
The Monday check protects the work of the first three weeks. If your Gmail spam rate creeps from 0.05% to 0.12%, you have time to find the cause before it reaches 0.3%. Find out when sales asks why nobody replies, and you're weeks behind.
Your first step takes five minutes. Open a copy of your last campaign in a Gmail inbox, choose "Show original" and check that all three authentication lines say PASS. If any line fails, or you'd rather hand the work off, send the result to our email marketing team and expect a reply within one business day.
Frequently asked questions
No mailbox provider publishes an official target for inbox placement. Watch the numbers they do enforce instead: a Gmail spam rate under 0.1%, authentication passing on every tool that sends for you, and a list you clean after each send. Seed-list tests from deliverability vendors can estimate your inbox rate, but they sample test mailboxes instead of your real readers.
Gmail and Yahoo don't require it below bulk volume, but you should publish one anyway. A DMARC record at p=none is a single DNS entry, and its reports show every service sending with your domain. It also covers you if one big campaign crosses the bulk line, since Gmail's bulk status never expires.
Anything at 0.3% or above is too high for Gmail and Yahoo, and Google asks you to stay under 0.1%. On a send to 10,000 people, 0.1% is 10 complaints. Microsoft publishes no number for Outlook.com, so use Gmail's 0.1% as your working limit for every provider.
Yes, and badly. Google tells senders not to buy addresses from other companies, and bought or scraped data is how senders hit the pristine and seeded spam traps that feed blocklists such as Spamhaus. Bought lists also bring hard bounces and complaints from people who never agreed to hear from you.
Expect about a week for authentication fixes to show and several weeks to rebuild a damaged reputation. Google says Postmaster Tools can take up to 7 days to reflect a fixed requirement, and Gmail bulk senders regain mitigation help only after 7 straight days below a 0.3% spam rate. A staged warm-up of your full list adds more weeks.