Why your emails go to Spam — and how to get out.

01Spam vs Promotions — the difference matters

People use "spam" as shorthand for anything that doesn't land in Primary. It isn't. Gmail (and every other major provider) treats them as distinct classifications with distinct causes.

Promotions means Gmail thinks your email is legitimate marketing that the recipient probably signed up for. It's delivered, findable, and counted. It just goes to a specific folder. Fix: change how you look and write, plus reputation work over a few sends. Covered in the Promotions guide.

Spam means Gmail thinks your email is unwanted, probably suspicious, and shouldn't be in front of the recipient at all. It's still delivered technically, but it lands in the spam folder — which almost nobody opens. Fix: something is actually broken with your setup, your list, or your sending pattern. This guide.

If you have real subscribers telling you "I found your email in my spam folder," take it seriously. That's not a soft signal. That's a mail provider making a strong call against you, and if you keep sending, the call gets stronger.

02The five things that get you spam-filtered

In roughly this order of frequency across the audits I've done:

Your auth stack is failing, not just misaligned

SPF and DKIM are the two authentication checks that say "yes, this domain really did send this email." If either fails outright — not "not aligned," but actually fails — mail providers can't verify the sender is who they claim to be. That's an instant confidence hit. If DMARC is set to p=reject on an unaligned domain, that's even worse. Some providers will block outright. Others will quietly send everything to spam.

Your sending IP is on a blacklist

Public blacklists like Spamhaus, SORBS, Barracuda, and a dozen others track IPs known to send unwanted mail. If you're sending from a shared IP that another customer got blacklisted, your mail carries the reputation of the whole IP. This is common on cheap shared hosting sending directly, and on ESPs that don't do IP hygiene.

You bought or scraped part of your list

This one bites people who ran a lead-gen play at some point and never fully cleaned it up. Purchased or scraped addresses often include spam traps — inboxes that mail providers set up specifically to catch senders using unclean lists. Send to a spam trap and your reputation drops fast. Send to several and you get blacklisted.

You had a complaint spike

One or two people marking your email as spam is background noise. A cluster of complaints in a short window is a red flag that most providers act on. This often happens after a launch — you sent to a lot of people quickly, they didn't remember signing up, they marked it as spam. Once the complaint rate crosses roughly 0.1% on Gmail, expect drop-offs. Cross 0.3% and expect the spam folder.

Your content or your links raise flags

Certain patterns trigger content-level spam filters: shortened URLs (bit.ly, tinyurl), domains that are on blacklists, sudden formatting changes from your baseline, embedded HTML that Gmail can't parse, obfuscated text, tracking pixels from services with a bad reputation. These are less common than the first four but they do happen — especially if you switched ESPs recently.

03How to diagnose which one is you

Before you spend a weekend fixing everything, spend an hour finding the specific cause. Order matters:

1. Check your DMARC reports if you have them. If you don't have a DMARC record with a rua address set up, do that first — you need the visibility. DMARC reports tell you exactly which messages passed and failed authentication, and where they came from. This alone rules in or out the auth-stack cause.
2. Look up your sending IP on the big blacklist checkers (MXToolbox is a decent free one). If you're on Spamhaus or SORBS, that's your problem, and no amount of copy work fixes it. You need to either delist through the provider's process, move to a clean IP, or (if it's a shared ESP IP) escalate to your ESP support.
3. Check your Google Postmaster Tools dashboard if you send more than 5,000 emails a day to Gmail. This is the closest you get to seeing what Gmail thinks of you. Domain reputation, IP reputation, spam-rate history, authentication pass rate. All right there. If your domain reputation reads "Low" or "Bad," you now know.
4. Segment recent send data by list source. If you have signup provenance recorded — which is a discipline you should build — pull the last 30 days of engagement broken down by where each subscriber came from. If the low-engagement / high-complaint segment is one specific source, that's your bad list.
5. Send a test to a fresh Gmail address from your usual sending setup, then check every header manually. Look for Authentication-Results. Verify SPF passes and aligns, DKIM passes and aligns, DMARC passes. Verify your Return-Path matches your From domain. This is a 10-minute check that catches a lot.

04The order to fix them in

Whatever you found, fix in this order. The order matters because reputation is cumulative — you can't rebuild it on top of a broken auth stack.

1. Fix authentication first. SPF and DKIM records must pass and align with your From domain. DMARC record published with rua reporting on. This is a one-day job with your DNS provider.
2. Get off the blacklist if you're on one. Each blacklist has its own delisting process; usually it involves proving you've fixed whatever got you listed. If it's an IP issue on shared infrastructure, move to a dedicated IP or a warmed subdomain.
3. Prune the list hard. Remove everything that hasn't opened or clicked in ninety days. Remove all bounces. Remove role addresses. Yes it will shrink your list. Your remaining list is now the one Gmail sees as engaged, and reputation works on engagement.
4. Stop sending to problem segments. If you traced complaints to one signup source, remove it from your active sends until you can rebuild trust. Yes that means fewer people getting your launches. It also means the ones who do get them count more.
5. Slow-warm your sending. Don't send to a big audience the day after you finish this list. For two to three weeks, send only to your most-engaged (30-day-active) subscribers. Then broaden. This is deliberate reputation rebuilding, and it works.

05Recovering after a spam-flagging incident

If you've been landing in spam for weeks or months, recovery takes six to twelve weeks of disciplined sending. That's not marketing speak — that's the memory horizon on major mail providers. You can shorten it by doing everything above cleanly, but you can't skip it.

The signal you're rebuilding is a specific one: your emails, sent to real people, get opened, clicked, replied to, and not marked as spam. Every campaign that produces those signals adds to the pile. Every campaign that misses does the opposite. If your open rate is 15%, don't send more to try to lift it — send less, to only the people who will open, until the classifier's read on you improves.

The mistake people make is trying to fix spam with more email. Fewer, better-targeted sends to a smaller, warmer segment does more than a full-list blast. When your reputation is back, you can widen.