Your launch email went to 20,000 people. Most of your Gmail readers never saw it.
Short answer: emails land in spam when providers stop trusting your sender reputation, which they build from complaints, bounces and whether people read you. The fix: authenticate, add one-click unsubscribe, cut dead addresses, ramp volume slowly and keep Gmail complaints under 0.1%.
We checked our own domain’s records to show the rules on a real setup. And one number in Google’s dashboard can look healthy while most of your mail sits in spam.
Why do emails land in spam? The five causes
Almost every spam-folder problem traces back to one of five causes. Check them in this order, because the first one can block you outright.
| Cause | What you notice | First fix |
|---|---|---|
| Failed or misaligned authentication | Bounces quoting 5.7.26 or 5.7.515 | Fix SPF, DKIM and DMARC alignment |
| Spam complaints | Gmail spam rate above 0.1% | One-click unsubscribe, no surprise sends |
| Dead and disengaged addresses | Hard bounces up, clicks down | Remove bounces, sunset non-readers |
| Volume spikes | 4.7.28 rate-limit errors, delays | Ramp up gradually |
| Misleading content or links | One campaign tanks, others don’t | Plain links, honest subject lines |
Authentication is the floor, and our step-by-step SPF, DKIM and DMARC guide has the exact DNS records. Everything below is about what still sends authenticated mail to spam.
Disclosure: the Brevo, Kit, SendGrid, Moosend and Hunter links here are affiliate links, so we may earn a commission at no cost to you.
Sender reputation: the score you never get to see
Sender reputation is each provider’s private judgement of whether people want your mail. Gmail, Outlook and Yahoo each keep their own, and none shows you the full number.
It sticks to two things. Domain reputation follows the domain in your From address and DKIM signature, wherever you send from. IP reputation follows the server that delivers the message.
On most email platforms you share that IP with other customers, so their habits affect you. Here’s the catch: your domain reputation travels with you, so switching platforms won’t wipe a bad one.
Do you need a dedicated IP?
Probably not, and the vendors don’t agree on the cut-off. SendGrid recommends one only above 50,000 emails a month. Brevo sets the bar at 100,000 a month, or three campaigns a week to 3,000-plus contacts.
A 20,000-subscriber weekly newsletter sends about 86,700 emails a month. That clears SendGrid’s bar and misses Brevo’s.
On Brevo it’s also a big-plan extra: a $251-a-year add-on sold only on Professional and Enterprise, and Professional starts at $499 a month. Our SendGrid review covers its Pro plan, which lets you add up to three IPs.
Our take: below about 100,000 emails a month, or with gaps between sends, stay on a shared IP. A dedicated IP that sends once a fortnight never builds a reputation, so every campaign starts cold.
The Gmail, Yahoo and Outlook rules you have to meet
All three big providers enforce the same core rules once you send about 5,000 emails a day to their users. Miss one and you get rejections or the spam folder, not a warning.
| Rule | Gmail | Yahoo | Outlook.com |
|---|---|---|---|
| SPF and DKIM both pass | Required | Required | Required |
| DMARC (p=none is enough) | Required, aligned | Required, must pass | Required, aligned |
| One-click unsubscribe | Required on marketing | Required | Easy opt-out |
| Honour unsubscribes | Within 48 hours | Within 2 days | Not specified |
| Spam complaint ceiling | Under 0.3%, aim 0.1% | Under 0.3% | Not published |
Two details trip people up. Gmail counts subdomains toward your main domain, so 2,500 emails from news.brand.com plus 2,500 from brand.com make you a bulk sender. And its FAQ says bulk-sender status is permanent once assigned.
Our weekly newsletter crosses that line on its first send if about 60% of the list uses Gmail. That’s 12,000 Gmail deliveries in one day.
Since November 2025, Gmail has been rejecting more non-compliant mail outright. Outlook.com bounces failing bulk senders with 550 5.7.515, naming the domain that failed.
What one-click unsubscribe looks like
It’s two headers your platform adds to each marketing email. Gmail’s unsubscribe button sends a POST to the link, and the reader is gone with no login and no confirmation page.
List-Unsubscribe: <https://example.com/unsubscribe/a1b2c3>
List-Unsubscribe-Post: List-Unsubscribe=One-ClickMost platforms add these for you. Check one real email before you trust that.
Spam complaints: why a low number can lie
Your spam rate is the share of people who click “Report spam” on mail that reached their inbox. Gmail calculates it daily and says anything above 0.1% already hurts bulk senders.
On 12,000 Gmail deliveries, 0.1% is 12 complaints and 0.3% is 36. Twelve annoyed people is a thin margin.
Now the twist. Google’s Postmaster Tools docs say the rate only counts mail that landed in the inbox. Nobody can report a message Gmail already filtered away.
Say Gmail sends 9,000 of those 12,000 straight to spam. The 3,000 that reach inboxes draw three complaints. Your dashboard shows a calm 0.1% while three-quarters of your mail sits in spam.
So read the spam rate next to your clicks, never alone. A flat spam rate during a slide in clicks is a warning, not a pass.
Complaints mostly come from three habits:
- Surprise frequency. A weekly list that goes daily during a launch. Yahoo’s guidelines name this one.
- A slow unsubscribe. If leaving takes four clicks, the spam button takes one.
- People who forgot you. Last year’s signup doesn’t recognise your name, so they report you instead of leaving.
Cross 0.3% and Google won’t offer delivery help until you stay under it for seven straight days. Pause the sends that caused it before you fix anything else.
List hygiene: bounces, spam traps and silent subscribers
A clean list is the cheapest deliverability fix there is. Every dead address you mail tells providers nobody’s looking after the list.
Remove hard bounces, addresses that don’t exist, after the first one. Soft bounces like a full mailbox get a few retries first. Most platforms handle both if you leave the setting on.
Platforms set their own ceilings. Moosend’s acceptable use policy allows hard bounces up to 3%, complaints up to 0.1% and one spam-trap hit. Our Moosend review covers what else the plan includes.
The dormant-list trap
Picture 8,000 contacts you haven’t emailed in nine months. Moosend’s 3% line allows 240 bounces. If one address in 25 has died since, that’s 320, and you’re over in a single send.
Old lists also hide recycled spam traps: abandoned addresses a provider turned into bait. One hit on a neglected list is enough to hurt.
How we’d bring it back:
- Run every address through a verifier first. Hunter checks them in bulk, and our Hunter.io review explains the credit costs.
- Send to the newest signups first, in batches of a few thousand.
- Ask the rest to confirm they still want your mail. Remove anyone who doesn’t open or click.
- Add a sunset rule. Ours: 90 to 180 days with no opens or clicks earns one last check-in, then removal.
Wait. Won’t that shrink your list?
Yes, and that’s the point. Gmail’s own guidelines suggest unsubscribing people who don’t read you.
Gmail and Yahoo also want every new address confirmed before you mail it. Double opt-in costs a few signups and blocks every typo and bot address.
Warm-up: new domains, new IPs and long breaks
Warm-up means raising volume slowly so providers learn your pattern before you hit full speed. Gmail warns that even doubling your usual volume overnight can bring rate limits.
You need it for a new sending domain, a new dedicated IP, or a list you’re mailing after a long gap. Brevo makes you re-warm a dedicated IP after 30 days without a send.
Brevo’s manual warm-up starts at about 3,000 emails a day and adds 15% daily, aimed at people who engaged in the last 30 days. Run the maths and our 20,000-person list is fully warmed on day 15, at about 21,200 sends.
SendGrid’s automated warm-up is slower on purpose. A new IP starts at 20 emails an hour, reaches 1,000 an hour on day 12 and finishes on day 41. Our Brevo review walks through that platform’s own warm-up options.
Cold outreach is a different job, with small daily caps per inbox and tools that trade warm-up emails between accounts. Our cold email outreach system guide covers that setup.
Common mistake: warming up with your oldest contacts. A ramp built on people who ignore you teaches providers the wrong lesson. Start with your most engaged readers.
Content and links: what filters actually look at
Content matters less than most guides claim. Filters care more about deception than about the word “free”.
Gmail’s guidelines flag these:
Re:orFwd:subject lines on emails that aren’t replies or forwards.- Display names like “Last Chance” or the reader’s own name, instead of who you are.
- Text hidden with HTML or CSS, and links whose destination doesn’t match their wording.
- Promotions inside receipts. Keep transactional and marketing mail on separate From addresses.
Links carry reputation too. A public link shortener shares its domain with every spammer who uses it, so link to your own domain and put your platform’s click tracking on a subdomain you control.
Our take on “spam trigger word” lists: mostly a distraction. Swapping “free” for “complimentary” won’t rescue a list full of complaints, and a list people want survives the word “free”.
How to find out why your emails go to spam
Work from the outside in: who’s affected, what the servers said, then what the message carries. Most problems show up by the third check.
Diagnose a spam-folder problem
Five checks, in order
-
Step 1 of 5
Find out who's affected
Send the same campaign to your own Gmail, Outlook and Yahoo addresses and note where each lands. If only one provider filters you, start with its rules.
-
Step 2 of 5
Read the bounce codes
Your platform’s bounce log quotes each server’s reply. The table below maps the common codes to a fix.
-
Step 3 of 5
Open Postmaster Tools
Verify your domain in Google Postmaster Tools and open the Compliance status dashboard. It marks each Gmail rule Compliant or Needs work, and fixes take up to 7 days to show.
-
Step 4 of 5
Read the message headers
In Gmail, open the email and choose Show original. SPF, DKIM and DMARC should say PASS, and the DKIM domain should be yours, not your platform’s.
-
Step 5 of 5
Check blocklists properly
Use the blocklist operator’s own lookup page or ask your platform. Lookups through public DNS resolvers can come back clean even when you’re listed, as we found below.
| Error | Where it comes from | What to do |
|---|---|---|
| 5.7.26 | Gmail: failed authentication | Fix SPF or DKIM, then DMARC alignment |
| 4.7.28 | Gmail: rate limit hit | Pause 10 minutes, resume on one connection |
| 550 5.7.1 | Gmail: sending IP suspended | Ask your platform to move you off that IP |
| 550 5.7.515 | Outlook.com: bulk domain failed auth | Make SPF, DKIM and DMARC pass and align |
What we found on our own domain
On 28 October 2026 we looked up droidcrunch.com’s live mail records through Google’s public DNS. It’s a real setup with three senders: Zoho for team mail, plus MailerLite and Brevo.
| Check | What we found | What it means |
|---|---|---|
| SPF | Zoho plus MailerLite, ending ~all | 6 of 10 allowed lookups used |
| DKIM | Zoho key 1,024-bit; Brevo keys 2,048-bit | All pass; Google recommends 2,048 |
| DMARC | p=none, reports to Brevo | Meets the bulk rule, blocks no spoofing |
| Blocklist via public DNS | Nothing returned | Inconclusive: Spamhaus’s test entry was clean too |
The blocklist check taught us the most. Spamhaus keeps a test domain that should always show as listed. Through Google’s resolver it came back clean, just like ours, so a clean public-DNS result proves nothing.
Brevo isn’t in our SPF record, and that’s fine. Brevo signs with our domain through DKIM, so its brevo1 and brevo2 keys carry DMARC alignment. One aligned pass is all DMARC needs.
What we didn’t do: send test campaigns, run seed tests or read Postmaster data for this post. Provider rules come from Google, Yahoo and Microsoft’s sender pages, and platform figures from Brevo, SendGrid, Kit and Moosend’s help docs, all checked on 28 October 2026.
The setting that matters on your email platform
Your platform can’t fix a bad list, but its domain settings decide whose reputation you build.
- Kit: until you add a verified sending domain, the hidden return-path is a Kit address, and your own DMARC can fail. Kit warns opens may dip for two to three weeks after you switch. Our Kit review covers the rest.
- Brevo: authenticate your domain so the DKIM keys are yours, and read the DMARC reports Brevo can collect, as ours does.
- SendGrid: set up domain authentication before the first send. Use automated IP warm-up only if a second, already-warm IP can take the overflow.
- Moosend: it won’t verify a sender until SPF, DKIM and DMARC all check out, and its 0.1% complaint limit matches Gmail’s target.
Frequently asked questions
Does landing in Gmail’s Promotions tab hurt email deliverability?
No. Promotions is a tab inside the inbox, not the spam folder, so the email was delivered. Don’t fight it with fake Re: subject lines or a display name that hints at a personal note. Gmail’s guidelines treat both as deceptive, and that costs you more than a tab does.
How long does it take to fix a bad sender reputation?
Expect weeks, not days. Google says fixes can take up to 7 days to show in Postmaster Tools, and delivery help returns only after seven straight days under a 0.3% spam rate. Our rule of thumb is two to four weeks of clean, steady sends to engaged readers.
Do transactional emails need one-click unsubscribe?
No. Gmail requires one-click unsubscribe only on marketing and promotional mail, so password resets, receipts and order confirmations are exempt. Send them from a different address than your newsletter and keep promotions out of them. Then a bad campaign can’t drag your receipts into spam.
Can I send my newsletter from a Gmail or Yahoo address?
Not reliably. When we checked, yahoo.com and aol.com published DMARC p=reject, so a platform sending as [email protected] fails DMARC and can be rejected. Google warns it will quarantine mail that fakes Gmail addresses. Send from a domain you own and authenticate it.
Should I send newsletters from a subdomain?
It keeps marketing and team mail apart, but it won’t dodge the rules. Gmail and Outlook count subdomain mail toward your main domain’s bulk total, and Postmaster Tools reports compliance for the main domain. Use a subdomain for tidy separation, not to stay under 5,000 a day.
Why do my emails go to spam in Outlook but not Gmail?
Each provider runs its own filters and keeps its own view of your reputation, so one can block you while another delivers. For Outlook, sign up for Microsoft’s SNDS to see your sending IP’s status and its Junk Email Reporting Program for complaints. Then look for 550 5.7.515 bounces.
Can a spam checker score guarantee inbox placement?
No. Content checkers test your DNS and scan the message, but they can’t see your complaint history or how Gmail users react to you. A perfect score on a tired list still lands in spam. Use the score to catch broken records, then trust seed tests and Postmaster data.
The bottom line
Email deliverability comes down to whether people want your mail. Providers measure that through complaints, bounces and engagement, and authentication only gets you checked.
Sending a newsletter? Add one-click unsubscribe, clean the list and keep your Gmail spam rate under 0.1%, read next to your clicks. Moving to a new domain or IP? Ramp up over two weeks or more, and stay on a shared IP until you send well over 100,000 a month.
One warning: a calm dashboard can hide mail already in spam. Your next step is to verify your domain in Postmaster Tools today, before you need it.
