Deliverability
Why your emails are landing in spam
Spam placement almost never has one cause — but it almost always has a first cause, and fixing in the right order saves weeks of guessing. Here are the ten that cover nearly every case we see, each with its fix, ordered roughly by how often it’s the actual culprit.
Rule of thumb: authentication first (it’s free and instant to check), reputation second (it’s slow but fixable), content last (it’s rarely the real problem, despite what everyone suspects first).
1. Missing or broken SPF, DKIM, or DMARC
The #1 cause, and the easiest to rule out. If your domain doesn’t publish working authentication records, receivers treat every message as unverified — and unverified mail from a small domain defaults to spam. Run your domain through the free email checker first; a missing record takes minutes to fix and solves a shocking share of “why are we in spam” cases. The full background is in SPF, DKIM, and DMARC explained.
2. Your domain or IP has no reputation yet
Deliverability is earned. A domain registered last month, or an IP that’s never sent mail, starts with zero trust — and zero trust means aggressive filtering while providers wait to see how you behave. The fix is patience plus consistency: send a steady, modest volume to people who actually engage, and reputation builds in weeks. Blasting a cold list from a brand-new domain does the opposite.
3. You're sending from a fresh IP with no warmup
Related but distinct: even an old domain on a new sending IP needs warmup — gradually increasing volume over two to four weeks so receivers learn the IP’s behavior. Jump straight to thousands of messages a day and you’ll trip volume-based filters on day one. If your provider doesn’t warm up new IPs for you, ask; it’s a standard, boring request.
4. Your list has bad addresses — or bought ones
Hard bounces are the loudest negative signal a sender can emit. Every message to an address that doesn’t exist tells receivers you don’t know who you’re mailing — the signature of a spammer. Purchased lists are all bad addresses plus spam-trap landmines. Clean the list (remove bounces and long-inactive addresses), and never buy one again. This single habit fixes deliverability for a lot of small businesses.
5. Nobody opens, replies, or unsubscribes
Gmail and Microsoft watch engagement more than any header. If your mail is systematically deleted-unread, ignored, or (worse) pulled out of spam by recipients, that pattern — not any rule violation — decides your placement. The fix is uncomfortable: send less, to people who want it, with subject lines that earn the open. A smaller engaged list outperforms a big cold one in every metric that matters.
6. You look like spam, statistically
Filters score content in aggregate, not by magic words. An image-only email, a link-to-text ratio that’s off, URL shorteners (heavily abused by spammers), ALL-CAPS subject lines, deceptive “Re:” tricks — each nudges the score. So does one giant image with no text. Write like a person, link like a person, and keep a real text version of everything.
7. You're on a blocklist
Spamhaus, Barracuda, SORBS, and friends publish lists of problematic IPs and domains. Landing on one gets your mail refused or filtered wholesale at every provider that subscribes — and most subscribe to at least Spamhaus. Check your sending IP and domain against the major lists; most have self-service removal and clear instructions. The faster lesson is what got you listed (usually causes 4 or 5) so you don’t boomerang.
8. Your DNS changed and nobody noticed
SPF and DKIM break quietly. Migrate CRM, switch email providers, let a domain lapse and re-register it — and yesterday’s working records are gone or orphaned. Authentication that passed for a year starts failing with no error visible on your side. If deliverability fell off a cliff after a vendor change, this is nearly always it. Re-run the checker and compare against what you published before the change.
9. You're sharing reputation with neighbors you didn't choose
On shared hosting or a cheap email add-on, your mail leaves the same IPs as everyone else’s on that server. One noisy tenant degrades everyone. You can’t fix the neighbor; you can move. Dedicated sending IPs (once you have volume to justify them) or a provider that isolates tenant reputation solves the class of problem.
10. You're triggering the wrong global rule
The boring catch-all: a misconfigured forwarder rewriting headers, a newsletter tool double-sending, an auto-responder loop. When nothing above fits, audit what actually leaves your domain — every tool, every automated message. The surprise is usually something a well-meaning teammate set up months ago and forgot.
Where to start, concretely
Do these four things, in order, before anything else:
- Check your domain’s records — SPF, DKIM, DMARC, MX, and MTA-STS in one pass. Fix anything red.
- Pull your bounce log and remove every hard-bounced address from every list you own.
- Check the major blocklists for your sending IP and domain; request removal where listed.
- For the next month, send only to people who’ve opened something from you recently. Engagement is the fastest reputation repair there is.
That sequence resolves the majority of spam-placement cases for small and medium teams. If you’d rather hand the whole problem to someone whose job it is — authenticated sending, monitored reputation, DMARC reports parsed for you — that’s exactly what SuperMailOS does, from $4 per mailbox per month. Back to all guides.