Last updated: July 2026.
Quick answer: Emails go to spam when mailbox providers don't trust the sender. The usual causes are broken authentication (SPF, DKIM, DMARC), a weak sending reputation, low engagement or spam complaints, and inconsistent sending from a domain that was never warmed up. It's a fixable signal, not bad luck.
If your emails just started going to spam, something changed. Either your sending changed, or the rules did, and since early 2024 the rules have changed a lot. Google, Yahoo, and Microsoft all tightened their requirements around authentication and complaint rates, so a domain that used to sail into the inbox can now get filtered for reasons that didn't exist a couple of years ago.
Most of the time the fix isn't one dramatic change. It's finding the signal that's off, correcting it, and then giving your reputation time to recover through steady, healthy sending.
If you keep asking why your emails go to spam, the answer is almost always one of a handful of signals, and if the reputation side is new to you, our email warm-up guide covers it in depth.
This post is about diagnosis: how to figure out which cause is sending your mail to spam, and exactly what to do about each one. That applies whether you're running cold outreach, a newsletter, or transactional mail like receipts and password resets, because warm-up and reputation are no longer a cold-email-only concern.
Mailbox providers score every message before it lands anywhere. You don't get to see the score, but it comes down to five things: does your mail prove it's really from you (authentication), does your domain have a track record of good sending (reputation), do people open and reply or do they hit "report spam" (engagement), does the message itself look trustworthy (content and formatting), and is your list clean or full of dead addresses (list quality).
Here's the part most guides skip.
These signals aren't equal, and they don't fail in isolation. Authentication is a gate. Pass it and you get considered. Reputation and engagement are what actually decide the inbox. That's why "I set up SPF and DKIM and I'm still in spam" is such a common complaint. You cleared the gate, but the room past it is judged on trust, and trust takes sending history to build.
Don't guess. Work through the signals from the most binary to the most gradual, because the early ones are yes-or-no and quick to rule out, while the later ones take observation.
Work through these one at a time. Fixing the right one is how you prevent your emails from going to spam for good, not just for a day, and each cause below comes with the specific fix.
SPF, DKIM, and DMARC are how you prove a message really came from your domain. Since February 2024, Google and Yahoo require them for bulk senders, and Microsoft has been tightening the same way. Without them, or with a misconfigured DMARC record, providers treat your mail as suspicious by default.
The fix is to publish all three records correctly and confirm they pass, not just exist. A DMARC policy that's set up wrong can send your own legitimate mail to spam, so check the actual result on a real message rather than assuming the record is fine.
Reputation is the track record your domain and IP build over time. Spam complaints, bounces, and sudden volume spikes drag it down. A brand-new domain has almost no reputation at all, which is why fresh domains struggle even when everything else is set up right.
You can't fix reputation with a single change. You rebuild it by sending consistently to people who engage, keeping complaints low, and giving it weeks, not days. This is the exact problem warm-up solves, which we'll get to below.
If your domain or sending IP lands on a blocklist, major providers will route you to spam regardless of how clean your setup is. Shared IPs are a common culprit, since someone else's bad behavior can taint the address you're sending from.
Check with a blocklist tool, and if you're listed, follow the delisting process for that specific list after you've fixed whatever triggered it. Mailivery monitors 70+ blacklists so you find out you're listed before your delivery falls off a cliff instead of after.
Filters read the message too. Misleading subject lines, a wall of images with barely any text, link shorteners, and a pile of exclamation points all raise the score against you. This matters less than authentication and reputation, but it's the easiest thing to fix.
Write the subject to match the content, keep a healthy text-to-image ratio, use full URLs from your own domain, and include a working unsubscribe link. Plain, honest messages clear filters far more often than heavily designed ones.
Engagement is the signal that separates the inbox from the spam folder once you're past authentication. If people don't open, reply, or click, providers read that as "nobody wants this." If they hit "report spam," that's worse. Google's threshold is a 0.1% complaint rate, and delivery suffers hard above 0.3%.
Send to people who actually want your mail, make unsubscribing easy so annoyed recipients leave instead of complaining, and prune addresses that haven't engaged in months. Fewer sends to an engaged list beats more sends to a cold one every time.
Sending to invalid or long-dead addresses drives up bounces, and hard bounces damage your domain reputation directly. A list you haven't cleaned in a year is quietly working against you.
Verify addresses before you send and remove hard bounces promptly. Mailivery includes email verification, so you can catch bad addresses before they cost you reputation.
A domain that jumps from zero to thousands of emails overnight looks exactly like a spammer. So does one that sends in erratic bursts. New domains and new sending tools both need a ramp-up period where volume climbs gradually and engagement stays high.
Skipping warm-up is the single most common reason new senders land in spam from day one. If you never warmed the domain, or you scaled volume too fast, that's likely your answer.
Once you're in the spam folder, fixing the underlying cause is only half the job. Providers have already learned to distrust you, and that verdict doesn't reset the moment you correct your SPF record. You have to rebuild the track record, which is what warm-up does.
Warm-up means sending a steady, gradually increasing stream of emails that get opened, replied to, and moved out of spam, so providers relearn that your mail is wanted. Across the mailboxes in our peer-to-peer network, the pattern we see most often isn't missing authentication. It's senders who fixed SPF, DKIM, and DMARC, saw nothing change, and assumed they were stuck. Authentication got them considered. It was engagement that eventually earned the inbox back, and that took weeks of consistent signals, not a switch they could flip.
That's where Mailivery fits. We warm up your mailbox by generating real interactions through a diverse peer-to-peer network of actual accounts, with AI-generated conversations rather than template replies, so the engagement looks natural to providers. When your warm-up mail lands in spam or promotions, the network pulls it back to the inbox and replies to it, which is the behavior that rebuilds reputation. Pricing is flat and starts at $29/mo, with unlimited mailboxes on every plan and no per-inbox fees, so warming one domain or twenty costs the same. Blacklist monitoring, email verification, and inbox placement testing are bundled in rather than sold as add-ons.
The causes are the same everywhere, but the providers weigh them differently, so it's worth knowing where you're actually landing.
Gmail leans heavily on engagement and its own reputation data through Postmaster Tools. If your Gmail recipients don't open or reply, Gmail notices fast, and it's strict about the 2024 bulk-sender rules. If you're going to spam in Gmail specifically, start with engagement and authentication.
Outlook and Microsoft 365 lean more on domain and IP reputation and are quicker to filter unauthenticated mail from unknown senders. New domains often struggle with Outlook longer than with Gmail. If Outlook is your problem child, focus on reputation, authentication alignment, and a slower ramp. The most reliable way to see the difference is to run an inbox placement test that shows where you land in each provider at once, instead of guessing from a single test account.
Gmail weighs engagement and its own reputation signals heavily, so low opens, few replies, or a spike in complaints will send you to Gmail spam even when other providers still deliver you. Check your standing in Google Postmaster Tools, confirm SPF, DKIM, and DMARC all pass, and focus on sending to recipients who actually engage.
Authentication is necessary but not sufficient. It gets your mail considered, but reputation and engagement decide the inbox. If everything authenticates and you're still in spam, look at your complaint rate, how engaged your recipients are, whether you're on a blacklist, and whether the domain was ever warmed up.
Run an inbox placement test, which sends to seed addresses across Gmail, Outlook, Yahoo, and others and reports where you land in each. Mailivery includes inbox placement testing in every plan, so you can see your placement across providers without pestering real contacts.
Plan for four to eight weeks of consistent, healthy sending. Reputation recovers gradually, not instantly, so slowing your volume, sending only to engaged recipients, and warming the domain back up all speed things along. There's no shortcut that skips the trust-rebuilding period.
Usually not. Spam placement follows your domain and sending reputation, not your provider, so moving to a new ESP with the same domain and habits lands you in the same place. Fix the underlying cause first, then a provider change won't undo your progress.
They can contribute, but content is a smaller factor than authentication and reputation. Misleading subject lines, link shorteners, and image-heavy messages with little text raise your spam score, so keep messages plain and honest. If content is your only issue, you'll usually see it as inconsistent placement rather than everything going to spam.
Yes, and it's often the missing piece. Warm-up rebuilds the sender reputation that landed you in spam by generating steady, positive engagement over time. It won't override a broken DMARC record or a blacklisting, so fix those first, then warm up to earn the inbox back.
Transactional mail hits spam for the same reasons marketing mail does: authentication gaps, a shared or low-reputation sending domain, or content that trips filters. Send transactional mail from a properly authenticated domain or subdomain, keep it distinct from bulk sending, and monitor its reputation separately.
There's no fixed number, because it depends on your domain's reputation and history. A warmed, trusted domain can send far more than a fresh one, and the danger isn't the total, it's the sudden jump. Ramp volume up gradually and watch your complaint and bounce rates as you scale.
Stop landing in spam. Mailivery warms up your mailboxes, monitors 70+ blacklists, and shows you exactly where your emails land, all on flat pricing with unlimited mailboxes. Start your free trial or see how warm-up works.
The easiest way to get responses to your cold emails.
