Opens sliding, or a subscriber told you they found you in spam? Here are the five real reasons any email lands in spam or the Promotions tab — and a 30-second test that shows exactly where your next send goes.
Most advice stops at 'clean your list.' Here's the honest version: five signals decide whether any email reaches Primary, Promotions or spam — and you can check every one of them on the exact email you're about to send.
Failed authentication is the most common reason legitimate email lands in spam: if SPF, DKIM and DMARC don't line up, mailbox providers can't confirm the message actually came from you, so they treat it as suspicious and filter it. It's invisible from your side and it fails silently, which is why it's the first thing worth checking.
Low engagement tells inbox providers your mail is unwanted: when opens and clicks drop and a handful of people hit 'mark as spam', Gmail and Outlook start routing you to spam to match how your readers behave. A list you bought, imported or grew with a giveaway is the fastest way to trigger it.
Heavy, promotional content pushes email toward spam and the Promotions tab: lots of links, big images, all-caps subject lines and 'too good to be true' offers read as bulk marketing, not a personal note. On its own it rarely means the spam folder — but stacked on a weak sender reputation, it tips you over.
An erratic sending reputation gets you filtered: sudden volume spikes, long silences followed by a big blast, a brand-new or shared sending domain, and mailing addresses that no longer exist all lower the per-domain score that decides whether you reach the inbox. Reputation decays slowly and recovers slowly, so the fix is never 'send more.'
The Promotions tab is not the spam folder: most of the time a newsletter that 'vanished' was quietly sorted into Gmail's Promotions tab, where real readers still find it. It's a different problem with a different fix — so before you rebuild anything, find out which one you're actually in.
Spam isn't one problem — it's five, and the fix depends on which one you've got. Start with what you're actually seeing.
A sudden drop usually means something changed — a DNS or domain change broke your authentication, a big import tanked your engagement, or a volume spike spooked the filters.
Forward the exact email that's failing to a test mailbox and you'll see which of the five is biting — authentication pass/fail, placement and content, all on your real send.
Nothing in the inbox, nothing in Spam, nothing in Promotions usually means the message was never accepted: it bounced, it was blocked, or your platform is still holding it.
That's a delivery failure rather than a filtering problem, and it has its own set of fixes.
If opens fell but no one's complaining, you're probably not in spam at all — you're in Gmail's Promotions tab, which real readers check but many skip.
That's a content-and-signals problem, not a reputation emergency.
Every sending platform has its own quirks — shared sending pools on starter plans, growth widgets, imported contacts — that change how the five causes play out.
Pick your platform for the version that matches how you actually send:
A spam score is a fine first read — it checks your message against a filter and flags the obvious content and authentication problems.
Get one in about 30 seconds, free.
A score tells you how you rate; a placement check tells you where you actually land — Primary, Promotions or Spam — across real Gmail, Outlook and Yahoo accounts.
Run the free check on your next send.
A perfect score on one filter can't see that Gmail sorted you into Promotions or that Outlook held back a new sender — a single mailbox isn't the same as real-inbox placement.
Here's the honest side-by-side of what each tool actually checks.
Two different failures get called the same thing. If the message reached the mailbox and got filed under Spam or Promotions, it was delivered — it just isn't where you looked, and the five causes above are your list. If it never arrived anywhere, the receiving server refused it or your sending platform is still holding it. That's a delivery failure, and it has its own fixes.
Almost every refusal comes back to your sending platform with an SMTP status code, and the first digit tells you most of what you need. 5xx is permanent: that server will not accept the message. 4xx is temporary: it's asking you to try again later. Open the campaign's bounce report before you change anything.
A hard bounce is a permanent decision by the receiving server: user unknown, mailbox not found, domain not found. Remove the address instead of retrying it — mailing addresses that no longer exist erodes the sending reputation that decides where the rest of your list lands. Checking whether an address is real before you send is a verifier's job, like ZeroBounce or NeverBounce. It isn't ours.
A soft bounce is temporary: a full mailbox, a server under load, rate limiting, or greylisting — where a receiver deliberately refuses the first attempt from an unfamiliar sender and accepts the retry a few minutes later. Your sending platform retries on its own for a day or two. It only becomes your problem when the same address soft-bounces send after send.
This is the one that feels like “none of my emails are going through”, because it hits the whole list at once instead of one address. The usual causes are your sending domain or IP sitting on a blocklist, or a DMARC policy set to p=reject while SPF or DKIM is failing. Worth saying plainly: p=reject doesn't send your mail to spam. It tells the receiver to refuse the message, so it comes back to you as a bounce, not as a complaint.
No bounce almost always means the message was accepted, and accepted means delivered. Before you touch a DNS record, have the recipient check the Spam folder and, on Gmail, the Promotions tab. If it's sitting in either one, this was never a delivery failure — it's a filtering problem, and the five causes at the top of this page are where to start.
“Not delivered” is sometimes “not sent.” Sending platforms spread large campaigns over hours, hold the first sends from a new account for review, and quietly pause a campaign when a domain check or a payment fails. The campaign's own send log answers this in seconds, and it's the cheapest thing to rule out first.
So you don't chase the wrong fix: everything on this page is about whether your sends reach the inbox. Checking whether an email address is real and deliverable is a different job — that's what verifiers like ZeroBounce and NeverBounce do. A clean list of valid addresses can still land in spam, and that's the problem we test.
You can rewrite subject lines and prune your list all week and still be guessing. Or forward your next send and see it: we open your real email in real Gmail, Outlook and Yahoo accounts and show the split — Primary, Promotions, Spam — plus a plain-English verdict (Safe to send, Risky, or Don't send) and the three fixes worth doing first. About 30 seconds, free. And hello@mailtester.ai is answered by a real person.
Forward your email → see where it landsIf you've ever searched "email tester," half the results check whether the address is valid. We do the other thing — whether the email itself will reach the inbox once you press send.
You upload a CSV of subscribers. The tool tells you which addresses bounce. Great for cleaning a stale list before a re-engagement send.
You forward one email — newsletter, launch, client note — to a one-time mailbox. We open it in real Gmail, Outlook, and Yahoo and tell you which tab it landed in, plus what to rewrite before you send it to your list.
Paste the mailbox above into the test-send field in Beehiiv, Kit, Substack, Mailchimp — or your own inbox. Hit go. We never see your subscriber list.
In real Gmail, real Outlook, real Yahoo. We watch where your email lands — Primary, Promotions, or Spam — using the same filters that decide whether your campaign worked.
Plain English. Three things to change, in priority order. Unlock the bundle and we generate a subject, body, and CTA rewrite in your voice — paste them back into your campaign before lunch.
Forward any email and get the score — free and unlimited. Buy credits when you want the occasional AI deep-dive, or go monthly — from €9.99 — if you send regularly. Cancel from the same screen you upgrade on.
Takes less time than picking a hero photo. Free, and no card at any point.