Email Deliverability: Why Your Emails Land in Spam (and How to Fix It)

Deliverability has to be the most overlooked problem in email. It’s no fun, it’s unsexy, it has nothing to do with design or copywriting.

Your campaigns may report that emails are ‘delivering.’ That feels reassuring. But ‘delivered’ doesn’t mean ‘in the inbox.’ It only means a server accepted the email.

Let’s keep your campaigns out of the spam folder, next to that long-lost Nigerian prince.

Which deliverability problem do you actually have? 

Before you start fixing things, figure out which problem you actually have. Match your symptom to the likely cause:

Found your row? Each one is covered in its own section below. Jump to yours.

If your opens and clicks dropped off a cliff 

A sudden drop usually means one of two things: your authentication broke, or your sender reputation took a hit. Check authentication first since it’s faster to diagnose.

Check your authentication right now. Send a test email to a Gmail address, open it, click the three dots → “Show original.” You’ll see pass or fail next to SPF, DKIM, and DMARC. If anything says fail, that’s your problem — head to the authentication section below to fix it.

If authentication is passing, check your reputation. Log into Google Postmaster Tools (free, takes five minutes to set up if you haven’t already). Look at your domain reputation — if it’s moved from High to Medium or Low recently, something you sent triggered complaints or spam-trap hits.

The recovery playbook:

1. Immediately stop sending to your full list. This is not optional. Every send to unengaged contacts at low reputation makes things worse.
2. Build a segment of your most engaged subscribers. These are people who opened or clicked in the last 30 days. This is your recovery list.
3. Send only to that segment for 2–4 weeks. Keep volume steady and predictable. No spikes.
4. Watch your Postmaster Tools reputation weekly. You’re looking for it to climb back from Low → Medium → High. This takes time — typically 2–6 weeks depending on how far it dropped.
5. Gradually expand your audience once reputation stabilizes. Add the 30–60 day engagers, then 60–90, pausing if reputation dips again.
6. Find the cause. While you recover, figure out what triggered the drop. Common culprits: a sudden volume spike, a campaign to a stale segment, a purchased list, or a change in your email platform settings that broke authentication.

If your engagement has been slowly declining 

A gradual decline over months almost always means list decay. Subscribers go inactive, change email addresses, or simply stop caring, and you keep mailing them as if nothing changed. Inbox providers notice.

How to stop the bleed:

1. Identify your inactives. Pull everyone who hasn’t opened or clicked in 90+ days. (Don’t trust open data alone. Use clicks and purchase activity too.)
2. Run a re-engagement campaign. Send 1–2 emails with a clear subject (“Still want to hear from us?”) and an easy one-click way to stay subscribed. Give it a week.
3. Suppress everyone who doesn’t respond. Not delete, suppress. You can always bring them back, but continuing to mail people who won’t engage is actively hurting your deliverability.
4. Tighten your collection. If you’re using pre-checked opt-in boxes at checkout, switch to unchecked or double opt-in. The list grows slower, but the subscribers actually want to be there.
5. Set up a sunset policy going forward. Automatically suppress subscribers after a set window of inactivity (90 days is common for ecommerce). This prevents the same problem from building up again.

If you’re fine in Gmail but landing in spam in Outlook (or vice versa) 

Each inbox provider scores your reputation independently. You can have a perfect record in Gmail and a terrible one in Outlook, or the other way around.

For Outlook/Microsoft issues:

• Sign up for Microsoft SNDS (Smart Network Data Services). It shows your IP reputation and complaint rates from Microsoft’s perspective.
• Microsoft tends to be stricter about volume spikes and authentication alignment. Make sure your DMARC alignment is set to relaxed at least, and that your sending IP has consistent volume patterns.
• Check if your IP is on any Microsoft blocklists — SNDS will tell you.

For Gmail issues:

• Google Postmaster Tools is your primary resource. It shows domain reputation, spam rate, authentication results, and encryption status.
• Gmail weighs engagement heavily. If Gmail recipients aren’t opening or clicking, Gmail learns that your email isn’t wanted — even if Outlook users love it.

For Yahoo/AOL issues:

• Yahoo uses the Complaint Feedback Loop — sign up for it. When a Yahoo user marks your email as spam, you’ll get notified so you can suppress them.

Run an inbox-placement test across all major providers before and after changes so you can see which provider you’re actually fixing.

If your bounce rate is high 

A high bounce rate signals to inbox providers that you’re not maintaining your list or that you’ve committed a cardinal sin of buying one.

Fix it fast:

1. Remove all hard bounces immediately. Most email platforms do this automatically, but check. A hard bounce means the address doesn’t exist and there’s zero reason to keep it.
2. Watch for patterns in soft bounces. A soft bounce (full inbox, temporary server issue) is fine occasionally. The same address soft-bouncing repeatedly is a dead address. Suppress it after 3 consecutive soft bounces.
3. Run your list through a verification service. ZeroBounce, NeverBounce, and Kickbox flag invalid, disposable, and risky addresses before you send. Do this before any large campaign and whenever you import a list.
4. Never, ever buy a list. Purchased lists are full of spam traps — addresses that exist solely to catch senders who didn’t earn their subscribers. One send to a trap-heavy list can tank your reputation overnight.
5. Add validation at signup. Use real-time email validation on your forms to catch typos and fake addresses before they enter your list.

If you’re landing in Gmail’s Promotions tab 

Take a breather, this is probably fine. The Promotions tab is not spam. It’s where Gmail puts marketing email, and shoppers know to check it when they’re looking for deals. Plenty of e-commerce revenue comes from the Promotions tab.

That said, if you want to increase your chances of hitting the primary inbox:

• Make emails look personal. Use plain text, a conversational tone, and a real person’s name in the From field
• Reduce the number of links and images. A single CTA performs better anyway.
• Engagement is the strongest signal. If people regularly open and click your emails, Gmail will start favoring the primary tab on its own.

Don’t burn hours trying to “hack” the Promotions tab at the expense of your actual email strategy.

If you have a new domain

A brand-new sending domain has no reputation. Not a bad reputation, just none at all. Inbox providers treat unknown senders cautiously. The fix is patience and a ramp-up plan.

A basic warm-up schedule:

1. Week 1: Send to your 50–100 most engaged subscribers per day. These should be people who will definitely open and click.
2. Week 2: Double the daily volume if your inbox placement and engagement look healthy.
3. Weeks 3–4: Keep doubling each week. Check your reputation in Google Postmaster Tools after every increase.
4. Week 5+: By now you should have enough volume history to send at your normal pace. If reputation dips at any stage, hold that volume for another week before increasing.

During warm-up:

• Send your best content. Open and click rates during warm-up directly shape your long-term reputation.
• Don’t send to your full list on day one. This is the single most common warm-up mistake.
• Set up Google Postmaster Tools and Microsoft SNDS before your first send so you have data from day one.

Pass the sender authentication requirements 

In 2024, Google and Yahoo stopped suggesting authentication and started requiring it. Microsoft followed in 2025. The rules officially start at 5,000 sends a day. Treat them as table stakes no matter your volume. Clear this bar or get filtered

• Authenticate your domain with SPF, DKIM, and DMARC. All three.
• Offer one-click unsubscribe in the email header, and honor it within two days.
• Keep your spam-complaint rate under 0.3%. Aim for under 0.1%. Above that, you’re in trouble.
• Use a valid sending domain with proper forward and reverse DNS, sending over TLS.

Most of this is set-and-forget once it’s done. But if your emails recently fell off a cliff, a broken or missing record here is the first suspect.

Authentication, in plain English 

Three acronyms that usually scare people off. They’re not as bad as they look.

• SPF is a guest list. It tells inbox providers which servers are allowed to send email for your domain. Not on the list? Looks like a forgery.
• DKIM is a tamper-proof seal. It signs your email so the receiver can confirm it really came from you and wasn’t altered in transit.
• DMARC is the rulebook. It tells providers what to do when SPF or DKIM fail (ignore, quarantine, or reject), and it sends you reports so you can see who’s sending as you. Start at monitoring, then tighten toward enforcement.

SPF, DKIM, and DMARC are small text records in your domain’s DNS settings. That’s the control panel where you bought your domain: GoDaddy, Namecheap, Cloudflare, Shopify, and so on

Think of DNS as your domain’s public address book. These records are just entries that tell the internet who’s allowed to send email as you.

The good part: you don’t write them from scratch.

1. Your email platform generates the exact records for you.
2. You paste them into your DNS settings.
3. You’re done in a few minutes.

How to check if yours are working right now. Send yourself a test email and check the headers (in Gmail: three dots → “Show original”). You should see PASS next to SPF, DKIM, and DMARC. You can also use free tools like MXToolbox — enter your domain and it’ll show you every authentication record and flag anything broken.

If “edit your DNS” sounds scary, it’s really just pasting a few entries into a settings page, once. Do it before you ramp up volume, not after something breaks.

Sender reputation: your sending credit score 

Every mailbox provider keeps a running score on your domain and IP. Good habits push it up: send to people who engage, keep complaints low, and bounce rarely. A steady sending rhythm helps too. Bad habits drag it down: blast a stale list, pile up spam complaints, or go quiet for months and then dump 50,000 emails at once.

The problem: that score is mostly invisible from where you sit.

Free tools to check your reputation:

• Google Postmaster Tools shows your Gmail domain reputation, spam rate, authentication results, and delivery errors. Reputation is rated High, Medium, Low, or Bad. This is the single most important free deliverability tool. If you set up nothing else, set up this.
• Microsoft SNDS — shows your IP reputation and complaint data from Outlook/Hotmail.
• MXToolbox — checks your domain and IP against common blocklists.

Paid inbox-placement testing. Want to see exactly where your email lands before you hit send? Tools like unspam.email and Reachly run inbox-placement tests against real inboxes. Reachly also builds authentication checks, inbox testing, and reputation into the campaign flow, which saves time across many campaigns.

Already damaged? Use the same playbook from the “opens and clicks dropped off a cliff” section above:

• throttle down
• mail only engaged contacts
• and rebuild gradually

Keep your list clean (and your bounces low) 

A big list full of dead addresses isn’t an asset. It’s a liability that drags your reputation down.

• Hard bounces are permanent (the address doesn’t exist). Remove them immediately, every time.
• Soft bounces are temporary (a full inbox, a server hiccup). Fine occasionally; a pattern means trouble.
• Spam traps are addresses that exist only to catch sloppy senders. You hit them by buying lists or never cleaning old ones. They poison your reputation fast.

The hygiene rules are simple. Verify addresses at signup. Use double opt-in when deliverability matters. Suppress people who haven’t opened or clicked in months. And never, ever buy a list.

A smaller list that engages beats a big one that bounces.

Stop trusting open rate (Apple broke it) 

Here’s a trap that catches even careful marketers. Apple’s Mail Privacy Protection auto-opens emails before a human sees them, and more than half of all opens now happen on Apple Mail. So your open rate is partly counting machines.

Don’t use open rate to tell whether you’re landing in spam. MPP inflates it, so a “healthy” number can mask a real problem, and a dip can be noise instead of a signal. Clicks are the honest read. Apple doesn’t fake those.

Watch clicks, conversions, your spam-complaint rate, and actual inbox-placement tests. Those tell the truth. Opens don’t anymore.

Content and the spam filters 

Reputation does most of the work, but content can still sink you.

Subject lines that trigger filters:

• ALL CAPS or excessive capitalization
• “RE:” or “FW:” on a cold send (deceptive, and filters know it)
• Rows of exclamation points or emoji in the subject
• Spam phrases like “Act now,” “Limited time,” and “100% free.” These matter less than they used to. But stacking several in one subject line still raises flags.

Email body red flags:

• One giant image with almost no text. Filters can’t read an image, so it just looks like an empty email trying to hide its content.
• A heavily imbalanced text-to-image ratio. Aim for enough real text that the email makes sense without images loading.
• Sketchy, shortened, or mismatched links (where the display URL doesn’t match the destination).
• No plain-text version of the email. Most platforms generate one automatically, but check.
• Embedded forms or JavaScript. These get flagged or stripped by almost every provider.

Deliverability quirks specific to ecommerce 

A few considerations for ecommerce-specific email sending:

• Use a dedicated sending domain — and split it. Some platforms send everyone from a shared pool, so a stranger’s bad behavior drags your reputation down. Once you have steady volume, move to a branded sending domain. Then split marketing and transactional mail onto separate subdomains: shop.yourstore.com for promos, mail.yourstore.com for receipts. That way a rough campaign week can’t block an order confirmation someone needs.
• Checkout opt-ins create junk subscribers. A pre-checked “send me marketing emails” box at checkout gets you a big list fast, but half of them never wanted to hear from you. That’s a spam-complaint factory. Unchecked opt-in or double opt-in after purchase builds slower but keeps your list healthy.
• Don’t shock the system at BFCM. Black Friday is the worst time to suddenly 10x your volume from a cold start. Ramp up in the weeks before, and prune your list first so you’re hitting engaged people during the one window that matters most.

How to know it’s actually working 

Track the numbers that reflect reality, not vanity:

• Inbox placement above 80%, and ideally higher (the share that actually lands in the inbox, not just the share a server accepted).
• Spam-complaint rate under 0.1%.
• Bounce rate under about 2%.
• Domain reputation at High in Google Postmaster Tools.

Make this a monthly check instead of a fire drill. Problems that show up early are cheap to fix. Problems that show up during Black Friday cost you revenue.

The essential deliverability toolkit 

Here’s everything referenced in this article in one place: