Why Are My Emails Going to Spam? A Troubleshooting Guide

Modern spam filters use hundreds of signals to determine whether an email belongs in the inbox or spam folder. Understanding these signals is the first step to fixing deliverability.

The major factors are:

• Sender reputation: Your IP and domain reputation scores (checked against blacklists and reputation databases).
• Authentication: Whether SPF, DKIM, and DMARC pass and align.
• Content analysis: The words, formatting, and structure of your email.
• Engagement history: How recipients have interacted with your previous emails (opens, clicks, replies, spam reports).
• Sending patterns: Sudden volume spikes, inconsistent sending patterns, or sending to many invalid addresses.

Email providers like Gmail, Outlook, and Yahoo each have their own spam filtering algorithms, so an email might reach the inbox at Gmail but land in spam at Outlook.

Missing or broken SPF record: If your domain doesn't have an SPF record, or if the sending server isn't listed in it, many providers will flag the email. Use LookMyIP's DNS Lookup to check your SPF record.

Missing DKIM signature: Emails without DKIM signatures are treated with more suspicion. Most email providers and marketing platforms support DKIM — make sure it's configured.

No DMARC record: Without DMARC, there's no policy telling receivers how to handle authentication failures. Even a p=none DMARC record is better than no DMARC at all.

SPF/DKIM alignment failure: DMARC requires that the domain in the "From" header matches either the SPF-authenticated domain or the DKIM-signing domain. Misalignment is a common cause of deliverability issues, especially when using third-party sending services.

Fix: Check all three records using LookMyIP's DNS Lookup tool. Send a test email to Gmail and inspect the "Show original" headers to see SPF, DKIM, and DMARC pass/fail status.

Blacklisted IP: If your sending IP is on a DNSBL (DNS-based Blackhole List), many receiving servers will reject or junk your email. Check using LookMyIP's Blacklist Checker.

Low domain reputation: Even if your IP is clean, email providers track domain reputation separately. A new domain with no sending history has a neutral reputation that needs to be built up gradually.

Shared IP issues: If you use a shared sending IP (common with email marketing platforms on their lower tiers), other senders on that IP can damage its reputation, affecting your deliverability.

Previous owner's reputation: If you purchased an expired domain or were assigned a previously-used IP, you may inherit negative reputation. Check your IP's reputation using LookMyIP's IP Reputation Checker.

Fix: Monitor your reputation with Google Postmaster Tools and Microsoft SNDS. If blacklisted, fix the root cause and request delisting. For critical email, consider a dedicated sending IP.

Spam trigger words: Words like "FREE!!!", "Act now!", "Click here!", and excessive exclamation marks raise spam scores. Write naturally and avoid aggressive sales language.

Image-heavy emails: Emails that are mostly images with little text look suspicious to spam filters. Maintain a healthy text-to-image ratio.

Broken HTML: Malformed HTML, inline CSS issues, and non-responsive designs can trigger spam filters. Use a reputable email template builder and test across clients.

Misleading subject lines: Subject lines that don't match the email content, use RE:/FW: prefixes deceptively, or contain ALL CAPS increase spam risk.

Missing unsubscribe link: Marketing emails without a one-click unsubscribe mechanism are increasingly penalized. Gmail and Yahoo require this for bulk senders.

URL shorteners: Using bit.ly or similar URL shorteners in emails is a major red flag because spammers frequently use them to disguise malicious URLs.

No warmup: Sending a large volume of email from a new IP or domain without gradually ramping up is the fastest way to land in spam. Warm up by sending to small, engaged audiences first and increasing volume over 2–4 weeks.

High bounce rate: Sending to many invalid email addresses signals poor list hygiene. Keep hard bounce rates below 2%. Remove bounced addresses immediately.

High spam complaint rate: If more than 0.1% of recipients mark your email as spam, your reputation drops quickly. Gmail's Postmaster Tools shows your spam complaint rate.

Purchased email lists: Never send to purchased or scraped email lists. The recipients didn't consent, bounce rates will be high, and spam complaints will destroy your reputation.

Inconsistent sending: Sending nothing for months and then blasting a large campaign looks suspicious. Maintain a consistent sending schedule.

Fix: Use double opt-in for list building, clean your list regularly, monitor bounce and complaint rates, warm up new IPs/domains gradually, and always provide easy unsubscribe options.

In February 2024 Google and Yahoo introduced enforced requirements for anyone sending more than 5,000 messages a day to their users. These moved a set of long-standing best practices into hard rules, and a great deal of mail that previously landed in inboxes started landing in spam or being rejected outright.

The requirements, which Microsoft substantially adopted in 2025:

Authenticate with SPF, DKIM and DMARC. All three. A DMARC record of p=none satisfies the minimum, but it must exist and must be aligned.

One-click unsubscribe. Marketing and subscription mail must include RFC 8058 headers, and the unsubscribe must be processed within two days:

List-Unsubscribe: <https://example.com/unsub?id=abc123>, <mailto:unsub@example.com>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

Both headers are required. List-Unsubscribe alone, which many senders had for years, does not satisfy the requirement.

Spam complaint rate below 0.3%, measured in Google Postmaster Tools. Above 0.3% and delivery degrades; sustained rates above that see mail rejected. The practical target is under 0.1%, because 0.3% is where enforcement begins rather than where problems start.

Valid forward and reverse DNS on the sending IP, with FCrDNS — the PTR must resolve to a hostname whose A record points back to the same address. Verify with the reverse DNS checker.

TLS for transmission. Opportunistic TLS is sufficient; plaintext SMTP is not.

Valid Return-Path, aligned with the sending domain, and it must accept bounces.

If you send at any volume, sign up for Google Postmaster Tools and Microsoft SNDS. They show the complaint rate and domain reputation that providers act on, and which no external checker can see.

Delivery problems generate specific diagnostics, and reading them is faster than working through a checklist. The SMTP response tells you both the severity and, usually, the cause.

The first digit is what matters most: 4xx is temporary and the sender will retry, 5xx is permanent and it will not.

Two of these deserve emphasis.

`550 5.1.1` must remove the address from your list immediately. Continuing to send to addresses that do not exist is one of the strongest negative reputation signals there is, because legitimate senders remove bounces and spammers do not. A hard bounce rate above 2% attracts filtering on its own.

Greylisting is not a problem. A receiver temporarily rejects the first attempt from an unknown sender, on the theory that real mail servers retry and much spam software does not. Delivery succeeds on the retry, typically within 5–15 minutes. Nothing needs fixing.

Full headers on a delivered message are equally informative. Look for the Authentication-Results header, which states plainly what the receiver concluded:

Authentication-Results: mx.google.com;
  spf=pass (google.com: domain of bounce@example.com designates 192.0.2.5)
  dkim=pass header.i=@example.com header.s=s1
  dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=example.com

That is the ground truth. Any external checker is an approximation of it.

Once authentication is correct, deliverability becomes almost entirely a question of who you send to and whether they want it. Providers increasingly weight engagement above every other signal.

Never buy or scrape a list. Purchased lists contain spam traps by construction, and hitting a pristine trap is close to an immediate listing. There is no sending technique that makes a purchased list deliverable.

Use confirmed opt-in for new subscribers. A confirmation email that requires a click before subscribing eliminates typo addresses, malicious sign-ups of other people's addresses, and bot submissions in one step. It reduces list growth numbers and improves every metric that matters.

Verify the list before a large send, particularly if it has been dormant. Verification services check syntax, domain validity, MX presence and known-trap membership. Removing 5% of a list to protect the other 95% is always the right trade.

Sunset unengaged subscribers. Someone who has not opened anything in twelve months is not going to. Continuing to mail them produces no revenue and steadily lowers your engagement rate, which providers use to decide inbox placement for everyone else on the list. Run a re-engagement campaign, then remove.

Segment by engagement when reputation is damaged. Sending only to your most active recipients for two to three weeks rebuilds positive signal faster than any other intervention.

Separate transactional and marketing streams. Use different subdomains — mail.example.com for receipts and password resets, news.example.com for campaigns — so that a marketing reputation problem cannot stop password reset emails from arriving. This is one of the highest-value structural changes available and it costs only DNS records.

Watch the complaint rate above all. One complaint per thousand messages is the working ceiling. If a campaign exceeds it, the problem is the content, the frequency, or the fact that recipients do not remember subscribing — not the mail server.

When mail is going to spam, working through possibilities randomly wastes days. This order resolves most cases quickly, cheapest checks first.

1. Is it universal or provider-specific? Send test messages to Gmail, Outlook, Yahoo and a corporate domain. Landing in spam everywhere points to authentication or reputation. Landing in spam at one provider only points to that provider's specific filters — very often Microsoft, which is markedly stricter than Google about new sending domains.

2. Check authentication on a real delivered message. Open the full headers and read Authentication-Results. Do not infer from a checker; read what the receiver actually concluded. Verify the configuration with the email authentication checker.

3. Check the sending IP and domain reputation. Run the IP through the blacklist checker and the reputation checker. Check Google Postmaster Tools for domain reputation, which is invisible externally and frequently the actual cause.

4. Check reverse DNS. A missing or mismatched PTR record on the sending IP causes rejection at many receivers and is trivially fixable — though only by whoever controls the IP block, meaning your hosting provider.

5. Only now, look at content. Spam-word lists are largely folklore at this point; modern filters are statistical. What genuinely matters is a plausible text-to-image ratio, no link shorteners, links whose domain matches the sending domain, a working unsubscribe, and no attachments in bulk mail.

6. Look at sending patterns. Sudden volume increases, a new IP with no warming, and irregular sending schedules all attract filtering independent of content.

The reason for this order is cost: steps 1 through 4 take minutes and cover the large majority of cases. Content rewriting takes days and is the least likely cause.