Why are my emails suddenly going to spam? The six causes, in order

"Suddenly" is the most useful word in the question. Emails that have always delivered fine don't drift into spam for no reason; something changed, recently, and your job is to find out what. The good news is that the list of changes that actually cause this is short. Six items cover nearly every case I see, and you can check the technical half of them on your domain right now, free, in about a minute.

Here they are, ordered by how often they turn out to be the answer.

1. A DNS record changed, broke, or vanished

The leading cause, and the least visible. Your SPF, DKIM or DMARC records live in DNS, and DNS gets edited: a website migration, a new registrar, an agency cleaning up "unused" TXT records, a colleague adding a new tool and accidentally creating a second SPF record (which makes SPF fail permanently for everything). Nobody who does this thinks they're touching email. Mail keeps sending afterwards; it just starts failing authentication, and placement sinks over days.

Ask yourself: did anything happen to the website, the domain, or the DNS in the past month? Migration, redesign, new IT provider, new marketing tool? If yes, you've probably found it. The health check reads your records as they are now and flags what's broken or missing.

2. The rules changed underneath you

Sometimes nothing changed on your side; the bar moved. The famous one: in February 2024 Gmail and Yahoo began requiring bulk senders to authenticate with their own domain, publish DMARC, keep complaint rates under 0.3%, and support one-click unsubscribe. Thousands of setups that were fine in January were substandard in February without a single record changing.

Enforcement of those rules has tightened in waves since, which is why "nothing changed but everything changed" keeps happening to new cohorts of senders. If your setup predates 2024 and has never been revisited, treat this as suspect number one, not number two.

3. You're on a blocklist

Blocklistings are sudden by nature: you're clean at breakfast and listed at lunch. Your own behavior can cause it (a burst to an old, cold list is the classic), but on shared ESP infrastructure you can also inherit it, when a stranger on your shared IP gets the whole neighborhood flagged.

This one you don't have to wonder about; it's checkable. The health check runs your domain against 24-plus blocklists in the same pass as the DNS checks.

4. Your list quality caught up with you

Mailbox providers watch how recipients treat your mail. Deleted unread, ignored, skipped, marked as spam: each signal teaches the filter. Send to a list that's grown stale and engagement sinks, which lowers placement, which sinks engagement further. A slow spiral that often looks sudden, because the visible symptom (a campaign that folders badly) arrives long after the cause started.

The tell: placement worsened gradually over months when you look honestly at the numbers, and the recent "sudden" drop coincides with a bigger-than-usual send or a re-activation campaign to old addresses. The fix is unglamorous: cut the dead weight, mail the people who read you.

5. The content of that specific campaign

Real, but overrated. People leap to blaming spam words because it's the one factor entirely in view. Filters today weigh sender reputation and authentication far more than vocabulary. Still, a campaign that's one giant image, stuffed with link shorteners, or missing a visible unsubscribe gives filters easy reasons.

The tell here is specificity: one campaign foldered while its neighbors delivered. If everything you send has started foldering, the cause is upstream, in items one through four.

6. A new tool entered the picture

Added a CRM, an outreach tool, a survey platform that sends "as you"? Every new sender either authenticates properly against your domain or chips at your reputation. Worse, setting one up is when SPF records get mangled (see item one). If the timeline of "we started using X" matches the timeline of "emails started foldering", you have your correlation.

How to actually diagnose yours

Work the list with the timeline. "When did it start?" crossed with "what happened around then?" solves most cases in one conversation. For the technical items (one, two, three), stop guessing and measure: run the free health check. It gives you a plain go/no-go verdict on your domain, the one most important fix if you're not good, and it detects which sending tools are configured on your domain, which regularly surprises people ("what's still sending as us from 2021?").

For a per-tool diagnosis, the ESP-specific checkers go deeper on the exact records your tool uses, and if a record you added won't show up, this troubleshooting guide covers the usual reasons in order.

The uncomfortable conclusion

Notice what five of the six causes have in common: they happen to you, silently, while you're busy running the business. Records drift, rules tighten, blocklists update, lists age, tools accumulate. Deliverability isn't a task you complete; it's a state that decays, which is the thesis this whole product is built on (the longer version lives here if you want it).

So fix today's problem, by all means. But the durable answer to "suddenly" is not checking harder once; it's not being the one who has to remember to check. Inbox Decay watches your setup continuously and emails you the moment something breaks, with the exact fix attached, free to start. The next silent change will still happen. The question is whether you hear about it from us on Tuesday or from your open rate in three weeks.