Why are my emails going to spam? Causes, diagnosis and 6 fixes
Emails usually go to spam for one of six reasons: failed authentication, a blacklist listing, a high spam complaint rate, damaged sender reputation, poor list quality, or a sudden volume increase. To find which one applies to you, run an inbox placement test first and read the pattern across Gmail, Outlook and Yahoo, rather than rewriting content or subject lines.
Key takeaways
- Most emails land in spam because of failed authentication, a blacklist listing, high complaint rates, damaged reputation, poor list quality or a sudden volume increase.
- The first step is always an inbox placement test, not changing content or subject lines, because the diagnosis determines every fix that follows.
- Fix authentication and clear blacklists before list hygiene, complaint rates and warmup, because no amount of copy iteration fixes a DKIM misalignment or a blacklist listing.
Why are my emails going to spam? The six common causes
Short answer: mailbox providers route mail to spam when authentication, blocklist status, complaints, reputation, list quality or sending pattern look risky. The table shows each cause, how it tends to appear, and how to confirm it.
| Cause | What it looks like | How to confirm |
|---|---|---|
| Failed or missing authentication | Spam at every provider, often right after a domain or sending-service change | Read SPF, DKIM and DMARC results on a delivered test message, not only in DNS |
| Blacklist listing | Sudden drop or blocks across providers while your sending tool still reports mail as sent | Check your domain and sending IP against Spamhaus, Barracuda and SURBL |
| High spam complaint rate | Gmail placement worsens first; engagement falls | Check spam rate in Google Postmaster Tools: 0.10% is the concern line, 0.30% brings routing to spam |
| Damaged sender reputation | Inbox at some providers, spam at others | Compare per-provider results in an inbox placement test |
| Poor list quality | High bounces, low opens, spam placement that tracks specific campaigns or lists | Review bounce rate and how many contacts have not engaged in 12+ months |
| Sudden volume increase | Problems begin the day volume jumps or a new IP or domain starts sending | Compare daily send volume against the date placement changed |
How to diagnose which cause applies to you
Start with where the mail actually lands, per provider. The pattern narrows the cause before you change anything.
| What a placement test shows | Most likely cause | Start with |
|---|---|---|
| Inbox at all providers | Likely engagement or list quality, not a filter problem | Steps 4 and 5 |
| Spam at one provider, inbox at others | Provider-specific reputation or complaints | Steps 5 and 4, then re-test |
| Spam everywhere | Authentication or reputation | Steps 2 and 3 first |
| Spam started when volume, domain or IP changed | Volume ramp | Step 6 |
Open rates cannot do this job: some recipients open mail in spam, and an unopened message looks the same whether it was filtered or ignored. How an inbox placement test works explains what it checks. For context on how hard cold sending is: GlockApps H1 2025 data, cited in our guide to how ISPs detect AI-generated email, put Gmail inbox placement for cold senders at 55.8%, Outlook at 28.7% and Yahoo at 44.5%.
What ISPs actually measure
Deliverability is not primarily a content problem. The factors that determine where your mail lands are mostly infrastructure and reputation — not whether your subject line has the word "free" in it.
| Factor | Impact | Notes |
|---|---|---|
| Authentication (SPF, DKIM, DMARC) | Critical | Missing or misaligned authentication causes immediate delivery failure at most providers. |
| Blacklist status | Critical | A Spamhaus listing blocks delivery at Gmail, Outlook, and Yahoo until removed. |
| Sender reputation (domain + IP) | High | Built over months of sending. Damaged by spam complaints, bounces, and volume spikes. |
| Spam complaint rate | High | Google's threshold: 0.10% warning, 0.30% routing to spam. |
| Bounce rate | Medium | High hard bounce rates signal poor list hygiene and damage domain reputation. |
| Sending volume and ramp | Medium | Sudden volume increases are treated as suspicious on any domain. |
| Email content | Lower | Content filters matter but are secondary to authentication and reputation signals. |
Six steps to stop emails going to spam
Follow these in order. Steps 1–3 address the most severe causes. Steps 4–6 address ongoing maintenance and scaling.
Step 1
Diagnose before you change anything
Run an inbox placement test at Gmail, Outlook, and Yahoo. If you are landing in inbox at all three providers, your deliverability problem is likely engagement or list quality — not a spam filter issue. If you are in spam at one provider and inbox at others, the problem is provider-specific. If you are in spam everywhere, authentication or reputation is the likely cause. The diagnosis determines everything that follows.
Run a placement test at /test before making any other changes.
Step 2
Fix authentication first
SPF, DKIM, and DMARC are the authentication layer that tells receiving servers your domain is legitimate and your DNS configuration authorises your sending service. Missing or misconfigured authentication is the most common cause of deliverability failure on new or recently migrated domains. SPF: verify your sending IP is covered. DKIM: confirm signatures are being added and aligned. DMARC: start with p=none to monitor, move to p=quarantine once confident.
Check authentication status on a delivered test message — not just DNS records.
Step 3
Check and clear blacklists
A Spamhaus, Barracuda, or SURBL listing will block or divert mail at major providers regardless of how good your authentication is. Check your sending domain and IP against the major blocklists. If you are listed, investigate the cause before requesting delisting — submitting a delisting request without fixing the underlying issue results in relisting, which extends the removal timeline.
Check domain and IP on Spamhaus ZEN, Barracuda, and SURBL.
Step 4
Clean your list
High bounce rates signal to ISPs that you are sending to contacts who do not exist or who have not engaged in years. Hard bounces should be removed immediately. Soft bounces after three failures should also be removed. For lists over 90 days old, consider re-engagement sequencing before cold outreach: send to the most recently active contacts first, monitor complaint and bounce rates, then suppress anyone who has not opened in 12+ months.
Remove hard bounces, suppress contacts not active in 12 months.
Step 5
Reduce complaint rates
Google's spam complaint threshold for bulk senders is 0.10%. Above 0.30%, Gmail begins routing mail to spam. Spam complaints are triggered when recipients click 'Report spam' — but ISPs also register implicit complaints: moving mail to junk, never opening, or deleting without reading. The most effective way to lower complaint rates is to send to people who want your mail, with a clear unsubscribe path and a reasonable sending frequency.
Add one-click unsubscribe, review sending frequency, segment by engagement.
Step 6
Warm up the domain if volume increased recently
A sudden jump in sending volume — from 200 to 2,000 emails per day — looks anomalous to ISPs even on a domain with established history. If you recently scaled up campaign volume or switched to a new sending IP, a warmup ramp is appropriate. Run warmup in parallel with real campaigns rather than as a separate phase: the positive engagement signals offset the volume increase.
If you recently scaled volume, run warmup alongside campaigns for 2–4 weeks.
Why order matters
The most common mistake in fixing deliverability is starting at step 5 or 6 — changing content, rewriting subject lines, adjusting sending frequency — when the actual cause is authentication or a blacklist listing at step 2 or 3. No amount of copy iteration fixes a DKIM misalignment.
Conversely, fixing authentication on a domain that is also blacklisted will not improve placement until the listing is cleared. Each step in the sequence removes a class of problem that would block the next step from working.
After completing steps 1–3, run another placement test before moving to list hygiene and complaint rate work. If you are now in inbox at all providers, the infrastructure fixes were sufficient — the ongoing steps (4–6) are maintenance, not urgent repair.
Sources and further reading
Thresholds and requirements above come from the providers and standards bodies themselves: Google's email sender guidelines (spam rate thresholds), RFC 7489 (DMARC) and Spamhaus (blocklist lookup). Related guides: email blacklist monitoring, fixing sender reputation and why a high warmup score can still land in spam.
Frequently asked questions
Why are my emails going to spam all of a sudden?
A sudden change usually points to something that changed on your side: a blacklist listing, an authentication failure after a DNS or sending-service change, a spike in spam complaints, or a jump in sending volume. Run an inbox placement test and check authentication on a delivered message first, because the pattern across providers tells you which cause applies.
Why do my emails go to spam even with SPF, DKIM and DMARC set up?
Authentication is necessary but not sufficient. Records that exist in DNS can still fail on the delivered message, and passing authentication does not offset a blacklist listing, a high complaint rate, a poor list or a volume spike. Check the results on a real delivered message, then work through the other causes.
Why do my emails go to spam in Gmail but not Outlook?
Each provider keeps its own reputation model for your domain. Spam at one provider and inbox at others points to provider-specific reputation or complaints, so check Google Postmaster Tools for Gmail and compare per-provider results in a placement test.
Does a high warmup score mean my emails will reach the inbox?
No. A warmup score is measured against a seed network, and synthetic seed mailboxes can inflate it. Only a placement test against real inboxes shows where mail lands.
Does changing my subject line or content fix spam placement?
Rarely on its own. Content matters, but authentication, blacklist status and reputation signals usually outweigh it, so rule those out first.
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Run free testFounder & CEO of InboxPlease. Over a decade building email infrastructure for SaaS businesses; writes about deliverability, inbox placement and sender reputation.