Your emails are most likely going to spam because of one of three things: the receiving provider can’t verify you’re really the sender (authentication), it doesn’t trust your sending history (reputation), or your recipients aren’t engaging and are reporting you (list and permission problems). Content and wording matter far less than most people assume. The fix starts with checking the message headers of an email that landed in spam, then working through the causes below in order.

First, diagnose: read the headers of a spammed email

Before changing anything, send a message to a Gmail, Outlook.com, or Yahoo address you control. If it lands in spam, open the full headers (“Show original” in Gmail, “View message source” in Outlook). Look for the Authentication-Results line:

Authentication-Results: mx.google.com;
       dkim=pass header.i=@news.example.com header.s=s1;
       spf=pass smtp.mailfrom=bounce.news.example.com;
       dmarc=pass (p=NONE) header.from=news.example.com

If you see fail, softfail, none, or permerror for any of these, start with causes 1 through 3. If everything passes, the problem is reputation, list quality, or content, so move on to causes 4 through 12.

Authentication causes

1. SPF, DKIM, or DMARC is missing or failing

Since February 1, 2024, Google requires all senders to personal Gmail accounts to use SPF or DKIM, and senders of 5,000+ messages a day to use SPF, DKIM, and DMARC. Yahoo set similar rules the same month, and Microsoft’s Outlook.com policies added requirements for domains sending over 5,000 emails a day from May 5, 2025. Mail that doesn’t comply can be junked or rejected; Microsoft’s rejection carries the code 550 5.7.515.

Fix: Publish SPF and DKIM for every service that sends as your domain, then add a DMARC record. Our SPF, DKIM, and DMARC setup guide walks through it.

2. Your From: domain doesn’t align

DMARC passes only if the domain that passed SPF or DKIM matches the domain in the visible From: address. A common failure: you send as you@example.com, but your ESP signs DKIM as esp-mail.net and uses its own bounce domain. Both SPF and DKIM “pass,” yet DMARC fails because neither aligns.

Fix: Set up custom DKIM signing with your own domain (d=example.com or a subdomain of it) in your ESP. Our post on DMARC alignment explains the rules.

3. Missing or mismatched reverse DNS (PTR)

If you run your own mail server, the sending IP needs a PTR record that resolves to a hostname, and that hostname must resolve back to the same IP. Google lists this as a requirement for all senders. ESPs handle this for you; self-hosted servers often get it wrong.

Fix: Ask your hosting provider to set the PTR record for your IP to your mail hostname, and make sure that hostname has a matching A or AAAA record.

Reputation causes

4. High spam complaint rate

This is the most direct path to the spam folder. Google tells senders to keep the user-reported spam rate below 0.1% and never reach 0.3% (Gmail sender FAQ). Yahoo’s limit is also 0.3%.

Fix: Check Google Postmaster Tools and your feedback loops. Find which campaigns, segments, or signup sources drive complaints and stop mailing them. Details in spam complaint rate.

5. Too many bounces

Mailing lots of addresses that don’t exist (550 5.1.1 User unknown) tells providers your list is old or poorly collected. Amazon SES, for example, recommends staying under 2% and puts accounts under review at 5%.

Fix: Suppress hard bounces automatically and clean lists before importing them. Our free email verifier flags malformed addresses, domains with no MX records, disposable domains, role addresses, and common typos like gmial.com or yaho.com. It doesn’t connect to the mailbox itself, so treat it as a first filter rather than proof an inbox exists.

6. Spam trap hits

Spam traps are addresses that never opted in, or abandoned addresses that were turned into traps. Hitting them signals poor list practices and can get you blocklisted. AWS notes that even a small number of spam trap hits can seriously hurt reputation.

Fix: Stop using purchased or scraped lists, remove long-inactive subscribers, and use confirmed opt-in.

7. You’re on a blocklist

If your IP or domain is on a widely used blocklist like Spamhaus, many servers will reject or filter your mail. A rejection message often names the list.

Fix: Check your IP and domain at Spamhaus’s reputation checker, fix the cause, and request removal. See email blacklists explained.

8. New domain or IP with no history, or a sudden spike

A brand-new domain sending thousands of emails on day one looks like a spammer, and so does an old domain that suddenly sends ten times its usual volume. Google’s guidelines say to increase volume slowly, send at a consistent rate, and avoid bursts.

Fix: Warm up new domains and IPs gradually, starting with your most engaged recipients.

9. Shared IP neighbors with bad habits

If your ESP puts you on a shared IP pool, other senders’ behavior affects that IP’s reputation. Google’s guidelines point this out and suggest confirming the shared IP isn’t on a blocklist. Domain reputation has reduced this risk, but it hasn’t removed it.

Fix: Ask your ESP about pool quality, authenticate with your own domain so your domain reputation stands on its own, and consider whether a dedicated IP fits your volume. See shared vs dedicated IP for email.

List and content causes

People who were added from a trade-show badge scan, a purchased list, or a pre-checked box don’t recognize you. They report spam instead of unsubscribing. Google specifically tells senders not to email people who didn’t sign up and not to buy lists.

Fix: Mail only people who opted in. Use confirmed opt-in for new signups. Be explicit at signup about what you’ll send.

11. Unsubscribing is hard

If people can’t find an unsubscribe link, “Report spam” is the next button. Bulk senders to Gmail and Yahoo must support one-click unsubscribe (RFC 8058) and show a visible unsubscribe link. Yahoo asks that requests be honored within 2 days; Google says 48 hours.

Fix: Add both headers and a visible link:

List-Unsubscribe: <https://example.com/u/8f3c2a...>, <mailto:unsub@example.com>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

The headers must be covered by your DKIM signature for one-click to work. See one-click unsubscribe and the List-Unsubscribe header.

12. Content and formatting red flags

Content is rarely the root cause on its own, but it can tip a borderline message into spam. Google’s guidelines call out:

Hiding content with HTML or CSS
Mixing promotional content into transactional messages, like ads inside receipts
Link text that doesn’t make clear where the link goes
Impersonating other domains or brands

Other common problems: a message that’s one big image with little text, broken HTML, link domains with poor reputation (including some public URL shorteners), and attachments in bulk mail.

Fix: Send well-formed HTML with a plain-text part, keep a reasonable text-to-image balance, use your own branded link-tracking domain, and keep transactional and marketing mail separate.

Quick-reference table: symptoms and likely causes

What you see	Likely cause	First thing to check
Spam at every provider, new domain	No history, volume spike	Warm-up plan, sending volume
Spam only at Gmail	Complaints or authentication at Gmail	Postmaster Tools spam rate and compliance
`550 5.7.515` from Outlook.com	Authentication requirements not met	SPF, DKIM, DMARC for the From: domain
`550 5.7.1` with a blocklist URL	Blocklist listing	Spamhaus and other list lookups
`dmarc=fail` but SPF and DKIM pass	Alignment	DKIM `d=` domain and Return-Path domain
Sudden drop after a list import	Bad or purchased data	Bounce and complaint rates for that segment
Transactional mail in spam	Shared domain with marketing	Separate subdomains per stream

A step-by-step recovery plan

Read the headers of a spammed message and fix any authentication failure first.
Check reputation sources: Google Postmaster Tools, Microsoft SNDS, Yahoo’s feedback loop, and a blocklist lookup.
Review your last few sends: which list, which segment, which signup source, and what the bounce and complaint rates were.
Pause risky segments such as old, imported, or never-engaged contacts.
Clean what’s left by removing hard bounces, complainers, and long-term inactives, and verifying any imported data.
Resume gradually, starting with recipients who engaged recently, and watch deferrals and complaints after every send.

If you’re about to send to an older list, run it through the verifier on this site first to strip out invalid syntax, dead domains, typos, and disposable addresses.

FAQ

Why are my emails going to spam when SPF, DKIM, and DMARC all pass?

Authentication only proves who you are; it doesn’t make providers trust you. If authentication passes, the cause is usually reputation (complaints, bounces, spam traps, blocklists), a volume spike, or recipients who don’t engage. Check Google Postmaster Tools and your complaint and bounce rates next.

Why do my emails go to spam in Gmail but not Outlook?

Each provider runs its own filters and keeps its own reputation data, so results often differ. A Gmail-only problem usually points to complaints or engagement among your Gmail recipients, which Postmaster Tools can show. Check whether your Gmail recipients are a different segment, such as older signups.

Do spam trigger words really send email to spam?

Single words rarely decide anything on modern filters. Reputation, authentication, and recipient behavior matter far more. That said, misleading subject lines, hidden text, and image-only messages can push a borderline message into spam, and deceptive subject lines are also prohibited by the FTC’s CAN-SPAM rules.

Will asking recipients to mark my email as “not spam” help?

It can help a little, because moving mail out of spam is a positive signal at providers like Gmail. But it won’t overcome a real authentication or complaint problem. Fix the root cause first, then encourage engaged subscribers to add you to their contacts.

How long until my emails stop going to spam after I fix the problem?

Authentication fixes can help as soon as the DNS changes spread. Reputation problems take longer, because providers need to see consistent good sending. Expect days to weeks, and keep volume to engaged recipients during that time.

Why Are My Emails Going to Spam? 12 Common Causes and Fixes