Why are my emails going to spam? A diagnostic checklist with free tools

Your emails go to spam when a mailbox provider decides, from many signals, that recipients probably don't want them. No single setting causes it. Usually it is a mix of missing authentication, a weak or damaged sender reputation, too many complaints, an old list, and sometimes the content itself.

The good news: almost every cause can be checked with free tools. This checklist goes through them in the order that finds most problems fastest. Work down it until something turns red.

First, confirm it really is spam placement

Before you change anything, find out where your mail actually lands.

1. Send a campaign or test to accounts you control on Gmail, Outlook.com and Yahoo.
2. Check the inbox, the spam or junk folder, and in Gmail the Promotions tab.
3. Check your platform's bounce log for messages that never arrived at all.

The Promotions tab isn't spam; it is where Gmail puts marketing mail by design. A bounce (the message was refused) is also a different problem from spam placement (it was accepted and filed as junk). Bounces come with an error code that usually tells you exactly what is wrong.

A few test accounts only give a rough picture, because placement is partly personal: someone who opens your mail every week may see it in their inbox while a new account sees spam. Use them to spot obvious problems, then confirm with the tools below.

1. Check authentication: SPF, DKIM and DMARC

Missing or broken authentication is the most common technical cause, and the easiest to check.

How to check: open a message you sent in Gmail, click More (the three dots) and choose Show original. The summary at the top shows SPF, DKIM and DMARC as PASS or FAIL. Then look at the Authentication-Results header:

Authentication-Results: mx.google.com;
  dkim=pass [email protected];
  spf=pass smtp.mailfrom=bounce.example.com;
  dmarc=pass header.from=example.com

• All three should pass.
• header.from (what readers see) should share its domain with the DKIM domain (header.i or header.d) or the SPF domain (smtp.mailfrom). If DKIM shows your email provider's domain instead of yours, DMARC alignment fails even though DKIM "passes".

You can also paste the full header into Google's free Admin Toolbox Messageheader tool for an easier read. Our SPF, DKIM and DMARC guide shows example records and how to fix alignment.

2. Check the Gmail, Yahoo and Outlook sender rules

Gmail and Yahoo set requirements for all senders in 2024, with stricter rules for bulk senders. Microsoft added rules for high-volume senders to Outlook.com in 2025. Mail that doesn't meet them can be filtered or rejected. In short:

• All senders (Gmail, Yahoo): SPF or DKIM, valid forward and reverse DNS for your sending IPs, and a spam rate below 0.3%. Gmail also requires TLS and properly formatted messages.
• Bulk senders (all three): SPF and DKIM, a DMARC record of at least p=none, and a From domain aligned with SPF or DKIM.
• Bulk marketing mail (Gmail, Yahoo): one-click unsubscribe and a visible unsubscribe link in the body.

How to check: Google Postmaster Tools has a Compliance status dashboard that marks each Gmail requirement as compliant or needing work. Google says changes can take up to seven days to show. The full table for all three providers is in our Gmail, Yahoo and Outlook sender requirements checklist.

3. Check one-click unsubscribe

If people can't leave easily, they press "Report spam" instead, and that hurts far more than an unsubscribe.

How to check: in Show original, look for both headers (defined in RFC 8058):

List-Unsubscribe: <https://example.com/unsubscribe/abc123>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

Then check the body has a clear unsubscribe link, and test that unsubscribing actually works. Yahoo requires unsubscribes to be honoured within 2 days; Gmail recommends 48 hours. Immediately is better.

4. Check your spam complaint rate

This is often the real answer. If more than a small fraction of recipients mark you as spam, providers move the rest of your mail there too.

How to check:

• Google Postmaster Tools: verify your domain with a DNS TXT record, then open the Spam rate dashboard. Google counts messages delivered to the inbox and then reported as spam, for DKIM-authenticated mail. Google requires staying below 0.3% and recommends below 0.1%. Low-volume days may not show data.
• Microsoft SNDS: if you control your sending IP (a dedicated IP), Smart Network Data Services shows each IP's complaint rate, defined as complaints divided by recipients. A rising complaint rate there is an early warning for Outlook.com placement.
• Yahoo: its Complaint Feedback Loop reports complaints back to you; most email platforms subscribe and unsubscribe complainers automatically.

Typical causes: mailing people who didn't clearly opt in, mailing too often, or a sudden send to contacts who haven't heard from you in a year.

5. Check your sender reputation

Reputation sums up your history. It is why the same email can land in the inbox for one sender and in spam for another.

How to check:

• Google Postmaster Tools has Delivery errors and Feedback loop dashboards next to spam rate. Google has retired the old Domain and IP reputation dashboards, so watch spam rate and delivery errors instead: a jump in either usually lines up with a send that went wrong.
• Microsoft SNDS shows a filter result for each IP you control: green when under 10% of mail is judged spam, yellow between 10% and 90%, red above 90%. Microsoft notes this isn't the same as inbox placement, but red is a clear warning.
• Blocklists: check your sending IP and domain on a public blocklist lookup. If you send from shared IPs, your email provider monitors this for you.

If reputation is low, slow down. A sudden jump in volume, a new domain without warm-up, or a burst of bounces all hurt it. See email warm-up for how to rebuild gradually.

6. Check list quality and bounces

Old and purchased lists are full of invalid addresses, people who forgot you, and sometimes spam traps: addresses that never signed up for anything and exist to catch senders with poor list practices.

How to check:

• Look at your hard bounce rate per campaign. A sudden rise means a bad segment or import.
• Look at when each contact last opened or clicked. A big block of contacts with no activity for a year is a risk.
• Ask where every segment came from. If you can't say how and when someone opted in, don't mail them.

What to do: remove hard bounces after the first one, send a re-permission email to long-inactive contacts and remove those who don't respond, and never buy lists. Yahoo tells bulk senders to monitor hard and soft bounces and inactive recipients, and to remove invalid addresses promptly. Email list cleaning goes step by step.

7. Check your content

Content matters less than most people think. Modern filters lean much more on reputation and recipient behaviour than on individual words, so swapping "free" for "complimentary" rarely fixes anything. But content can still tip a borderline sender into spam.

Check for:

• One big image and no text. Keep real text in the email: offers, prices and links should be readable even with images off.
• Link shorteners and mismatched links, where the visible text shows one domain and the link goes to another.
• Links to domains with a poor reputation, including any you don't control.
• Misleading subject lines, like a fake "Re:" or "Your order" on a promotion. These drive complaints.
• A From name readers don't recognise. Use your brand name consistently.
• Broken HTML, or messages copied from a word processor with hidden formatting.

Example of the difference:

8. Check volume and sending patterns

Sudden spikes look like abuse. Google advises increasing volume slowly, sending at a consistent rate and, if bounces or deferrals start, cutting volume until errors drop.

How to check: compare the campaign that went to spam with your normal volume. If you sent five times your usual amount, or sent from a new domain or platform for the first time, that is likely part of the answer.

Also check frequency. If you went from one email a week to one a day, complaints usually follow.

9. Check that cold email isn't on your main domain

If anyone in your company sends cold outreach from your main domain, its complaints and bounces count against the same domain as your newsletter and receipts. Move outreach to separate domains and mailboxes. The cold email deliverability guide explains the setup.

Quick reference: symptom and likely cause

How EterMail helps

EterMail is our product. It checks that your sending domain is verified and your postal address is set before a campaign can go out, adds a footer with that address and an unsubscribe link, adds one-click unsubscribe headers (RFC 8058) to marketing email, and sends at most one marketing email per contact per 24 hours, re-checking consent at send time. Sending pauses automatically if bounces or complaints spike. Cold outreach runs from separate mailboxes and domains with gradual ramp-up and daily caps. AI can also make the pictures: on-brand banners, or scenes built from your real product photo, with an optional short greeting. Prices, discounts and links stay in the email text, not in the picture.

For a fuller picture of how mailbox providers decide, read our email deliverability guide.

FAQ

Why are my emails suddenly going to spam?

A sudden change usually has a sudden cause: a much larger send than usual, a new or changed sending domain, a DNS change that broke SPF or DKIM, or a send to an old segment that produced bounces and complaints. Check Show original for authentication first, then Google Postmaster Tools for a spike in spam rate or delivery errors around that date.

Why are my emails going to spam in Gmail but not Outlook?

Each provider keeps its own reputation data and filters, so placement can differ. Gmail weighs its own users' spam reports and engagement heavily. Check Google Postmaster Tools for your spam rate and compliance status, and make sure you meet Gmail's sender requirements, including DMARC alignment and one-click unsubscribe for bulk mail.

How do I check if my email is going to spam?

Send to test accounts you control at Gmail, Outlook.com and Yahoo and check every folder, but treat that as a rough check because placement varies by recipient. For the real trend, use Google Postmaster Tools for Gmail, Microsoft SNDS if you control your sending IP, and your platform's bounce and complaint data.

Do spam trigger words still matter?

Much less than they used to. Filters rely mainly on sender reputation, authentication and how recipients react. Avoid misleading subject lines and image-only emails, but don't expect word swaps to fix a reputation or complaint problem.

How do I stop my emails from going to spam?

Authenticate with SPF, DKIM and DMARC, meet the Gmail, Yahoo and Outlook sender rules, email only people who opted in, make unsubscribing one click, remove bounces and long-inactive contacts, and grow volume gradually. Then watch your spam rate in Postmaster Tools and keep it under 0.1%.

Can a recipient's actions move my email out of spam?

Yes, for that recipient. Marking a message "Not spam" or adding you to contacts helps future placement in their mailbox, and Google counts mail moved out of spam as delivered to the inbox when it calculates spam rate. It doesn't fix a wider problem, though; that takes the checklist above.