Emails going to spam almost always trace back to one of five things: failed authentication, a damaged sender reputation, a blocklist listing, a weak or unengaged list, or content and links that look suspicious. This checklist helps you tell which one you have, shows the order to check them in and gives the fix for each.
Fix before you resend. Sending more mail while the cause is still there makes the problem worse. Pause large sends, send only to your most engaged recipients while you investigate and change one thing at a time so you know what worked.
The short version
- Find out where the mail went. Rejected, delivered to spam, filed under Promotions or never sent: each has a different cause.
- Check authentication first. SPF, DKIM and DMARC must pass and align. It is the fastest check and the most common cause.
- Check reputation and blocklists. Use Google Postmaster Tools and a blocklist lookup for your IP and domain.
- Check the list. Bounces, complaints and unengaged recipients tell receivers whether your mail is wanted.
- Check content and links. Look for deceptive wording, mismatched or shortened links and missing plain text.
- Recover gradually. Fix, reduce volume to engaged recipients and ramp up again.
Step 1: Work out what actually happened
The word spam covers several outcomes. Start with your delivery log in MigoSMTP and match what you see to the table below.
| What you see | What it means | Where to look next |
|---|---|---|
| Delivered, but recipient finds it in spam | The receiver accepted the message and filtered it | Authentication, reputation, engagement, content |
| Delivered, but in Promotions or Updates | Normal tab sorting at Gmail, not a spam problem | Content style and message purpose |
| Rejected with a 5xx code | The receiver refused the message | Read the code and text: see the bounce code guide |
| Deferred with a 4xx code | The receiver is slowing you down | Volume, reputation and sending rate |
| Accepted but never seen | Silently dropped or quarantined | Ask the recipient to check quarantine, then test other addresses |
Step 2: Check authentication
Send a test message to a Gmail address, open Show original and look at the top summary. SPF, DKIM and DMARC should all show PASS. A failure, or a pass that does not align with your From domain, is a likely cause, and Gmail, Yahoo and Outlook.com now expect all three from bulk senders. See how to authenticate a sending domain and the bulk sender requirements.
| Check | Pass looks like | If it fails |
|---|---|---|
| SPF | PASS, one record, fewer than 10 lookups | Merge records and add every sending service |
| DKIM | PASS with d= set to your own domain | Publish the selector record and sign with your domain |
| DMARC | PASS because SPF or DKIM aligns | Align the Return-Path or DKIM domain with the From domain |
| PTR record | The sending IP resolves to a host name that resolves back | Ask your provider to set reverse DNS |
| TLS | Mail sent over an encrypted connection | Check the delivery log for the TLS version |
Step 3: Check reputation and blocklists
Receivers keep a score for your sending domain and your IP address. The score rises with consistent volume, low bounces, few complaints and recipients who open, click and reply. It falls with the opposite.
- Google Postmaster Tools: shows spam rate, authentication and delivery errors for mail to Gmail users.
- Microsoft sender support: lets you check how Outlook.com sees your IP and apply for help.
- Yahoo sender tools: a complaint feedback loop shows which messages recipients reported.
- Blocklist lookups: check your sending IP and domain on the major lists such as Spamhaus. Not every list matters, so focus on the ones receivers actually use.
A listing is a symptom. Blocklists list you because of something you did or something that was done with your account, such as a compromised credential. Remove the cause first. Then follow the process on that list to request removal.
Step 4: Check your list and engagement
Mailbox providers watch how recipients react. A list full of old, wrong or unwilling addresses produces bounces, spam traps and complaints, and those are the strongest negative signals.
| Signal | Healthy | Warning |
|---|---|---|
| Hard bounce rate | Under 1 to 2 percent | Over 2 percent, or a sudden jump |
| Spam complaint rate | Under 0.10 percent | Over 0.10 percent, never reach 0.30 percent |
| Unengaged contacts | Removed after several months | A large share of the list has not opened for a year |
| List source | Opted in, ideally confirmed | Purchased, scraped or very old |
| Unsubscribe | Easy to find and one click | Hidden, so recipients use the spam button |
What to do
- Suppress hard bounces and addresses that keep soft bouncing.
- Send only to recipients who engaged in the last 90 days while you recover, then widen gradually.
- Add double opt-in for new sign-ups so typos and fake addresses never reach the list.
- Make the unsubscribe link easy and add one-click headers, as in the one-click unsubscribe guide.
Step 5: Check content and links
Content alone rarely decides placement, but it can tip a borderline sender into the spam folder. Check the following:
- Subject and sender name: accurate, not misleading, and consistent from send to send.
- Links: use your own domain for tracking links. Avoid public URL shorteners and links whose visible text points to a different domain than the real destination.
- Images: do not send an email that is one large image. Keep a healthy balance of text and images and add alt text.
- Plain text version: include a plain text part alongside the HTML.
- HTML quality: valid markup, no hidden text, no scripts or forms.
- Attachments: avoid unexpected attachments in marketing mail, and avoid risky file types.
- Footer: include your business name, a postal address where the law requires one and an unsubscribe link.
Step 6: Check your sending pattern
| Pattern | Why receivers dislike it | Fix |
|---|---|---|
| Sudden volume spike | Looks like a compromised account | Raise volume in steps, as in the warm-up guide |
| New domain or IP at full volume | No history to trust | Warm up before sending in volume |
| Long silence, then a big send | Reputation fades when you stop | Send regularly, or restart at lower volume |
| Mixed transactional and marketing mail | Marketing complaints hurt receipts and resets | Use separate subdomains and, at scale, separate IPs |
| Sending to the whole list every time | Low engagement drags reputation down | Segment by interest and recent activity |
Symptom to cause: a quick reference
| Symptom | Most likely cause | First action |
|---|---|---|
| Spam at every provider, started after a DNS change | Broken SPF, DKIM or DMARC | Check the headers of a test message |
| Spam at Gmail only | Gmail reputation or spam rate | Open Google Postmaster Tools |
| Spam at Outlook.com only | Microsoft filtering or authentication level | Check for 5.7.515 style errors and the Microsoft sender portal |
| Spam started after a big campaign | Complaints from an unengaged segment | Pause, then send only to engaged recipients |
| Rejections with a blocklist name in the text | Listing on a blocklist | Find the cause, then request removal |
| Spam only for one newsletter | Content or segment problem | Compare it with a stream that works |
A two-week recovery plan
| Days | Do this | Aim |
|---|---|---|
| 1 to 2 | Pause large sends. Fix authentication and any listing cause | All three checks pass |
| 3 to 5 | Send to the most engaged 10 percent of the list | Placement and complaint rate improve |
| 6 to 9 | Widen to recipients active in the last 90 days, in steps | Complaints stay under 0.10 percent |
| 10 to 14 | Resume normal segments with a re-engagement flow for the rest | Stable inbox placement |
Still landing in spam? Send us the headers of a test message and the date the problem started and we will help you find the cause.
Further reading and sources
Frequently asked questions
Why are my emails going to spam all of a sudden?
A sudden change usually has a trigger: an authentication record that changed or broke, a bigger or older list than usual, a jump in volume, a new sending domain or IP, a campaign that drew complaints, or a listing on a blocklist. Compare the date of the first problem with what changed in your setup and your sending.
How do I know if my emails are going to spam?
Send a test to your own accounts at Gmail, Outlook and Yahoo and check where it lands. Review the bounce and deferral codes in your delivery log, and watch Google Postmaster Tools for spam rate and reputation. Seed tests are only a rough guide, because real inbox placement depends on each recipient and their past behaviour.
Is a spam score tool reliable?
Spam score tools check obvious issues such as missing authentication or broken links, and they are useful for that. They cannot see your reputation or how recipients treat your mail, so a good score does not guarantee the inbox and a poor score is not always the cause of spam placement.
Do spam trigger words really matter?
Much less than people think. Modern filters weigh reputation, authentication, engagement and link quality far more than single words. Deceptive subject lines, all capitals and heavy punctuation can still hurt, mainly because they raise complaints.
Can a blocklist listing send my mail to spam?
Yes. Receivers often check the sending IP, domain and links in the message against blocklists. A listing on a major list can lead to rejection or spam placement. Find out why you were listed, fix the cause and then request removal; removal without a fix usually leads to relisting.
Why do my emails go to the Promotions tab?
Gmail sorts mail into Primary, Promotions and other tabs based on content and sender behaviour. Promotions is not the spam folder, and it is normal for marketing messages. Transactional messages that land there often look promotional: reduce marketing language, images and multiple calls to action.
How long does it take to recover from spam folder placement?
It depends on the cause. A fixed authentication problem can recover within days. A damaged reputation usually takes several weeks of clean sending to a small, engaged audience before volume can rise again. Avoid sending large campaigns until you see placement improve.
Should I buy a new IP address or domain to escape spam placement?
No. A new IP or domain starts with no reputation, and sending the same kind of mail to the same list will damage it as well. Fix the cause first, then use a proper warm-up plan on whatever infrastructure you use.
Do open rates tell me if I am in spam?
Only roughly. A sharp drop in opens at one mailbox provider while other providers stay steady is a strong hint. Open tracking is also affected by privacy features that preload images, so use it together with click, bounce and complaint data.
What is a spam trap?
A spam trap is an address that does not belong to a real subscriber and is used to catch senders with poor list practices. Pristine traps were never used by a person, and recycled traps are old abandoned addresses that were later reused. Hitting traps damages reputation, which is why old, purchased or scraped lists are risky.