Start here: five questions
Where is the mail landing?
If you are guessing, run a placement test first; it answers this per provider in minutes.
The ten reasons emails go to spam
1. SPF, DKIM or DMARC fails or does not align. The filters check authentication first, and since 2024 Google, Yahoo and Microsoft reject on it. A record can exist and still not align with the From domain. Run the auth checker for the records and the auth checker on a message's headers for alignment.
2. The sending domain has no history. A domain under 30 days old, or one that never sent, gives the receivers nothing to trust, and they filter on caution regardless of the records. The fix is warming for 21 days before any outreach, and a placement test at the end.
3. The sending IP has a bad neighbour. On a shared IP at a relay or a small provider, someone else's spam is your listing. The blacklist checker shows the IP's listings; on Google Workspace and Microsoft 365 the IPs are the provider's and managed.
4. The domain is on a blacklist. The Spamhaus DBL, SURBL and URIBL list domains; the IP lists list addresses. A listing on an enforced list is the whole answer until it is removed, and each list's delisting guide gives the operator's own process.
5. The content reads like spam. Capitals and exclamation marks in the subject, an image-only body, a high link-to-text ratio, links to domains the filters already flagged, a tracking domain shared with other senders. None is fatal alone; together with a thin reputation they are. The template analyzer names the evidence for each finding.
6. The volume jumped. A domain that sent thirty a day and sends three hundred today reads as a spam pattern, and Google returns 421 4.7.28 for it. Volume climbs on a curve; the cold email volume page has the arithmetic.
7. The list has dead addresses. Mail to addresses that do not exist is the signature of a bought list, and the bounce rate is what the receivers read. Verify before the first send, remove every hard bounce, and read the bounce rate guide for the thresholds.
8. Recipients do not engage, or they complain. Filters score recent behavior: mail deleted unread, ignored, or reported. Google's spam-rate line is 0.10% in Postmaster Tools and 0.30% is the point past which it will not mitigate. Engagement compounds in both directions, which is why a domain that has stopped landing keeps getting worse.
9. The links go through a public shortener. bit.ly, tinyurl and their kind are abused by spam, so filters discount any URL on them. Use a subdomain you own; do links affect deliverability covers the rest.
10. The sending pattern reads as automation. Every message at the same minute, the same template from every mailbox, the same footprint across a domain: filters are trained on exactly that. Warming that reads as a team of different people, with an AI Agent on each mailbox, is the answer to this one.
How to diagnose which one is yours
In order; stop at the first failure.
- Authentication. The auth checker for SPF (with the ten-lookup limit), DKIM, DMARC, MX and BIMI; the auth checker on a message for alignment.
- Blacklists. The domain and its IPs against the enforced lists. A listing stops the diagnosis until it is removed.
- Placement per provider. The Free Deliverability Test, or mailboxes you control at Gmail, Outlook.com and a Microsoft 365 tenant. Spam everywhere is the sender; spam at one provider is that provider's record of you.
- The consoles. Postmaster Tools for the spam rate and the domain tier; SNDS for the IPs at Outlook.com. The Postmaster page reads the tiers.
- Content. The template analyzer on the exact message that failed.
- Engagement by mailbox. If one mailbox drags the domain, its list, its volume or its agent's persona is the problem, not the domain's.
The fix for each
| Cause | Fix | Where to check |
|---|---|---|
| Authentication fails | Publish or repair the records, confirm alignment on a real message after propagation | Auth checker, auth checker |
| No domain history | Warm for 21 days before outreach; keep warming after | Placement test |
| Bad shared IP | Move to the provider's own sending, or a dedicated IP with PTR | Blacklist checker |
| On a blacklist | Fix the cause, then the operator's own delisting process | Delisting guides |
| Content signals | Rewrite for one person; own tracking domain; links you would send from | Template analyzer |
| Volume jump | Back to the curve; add warmed mailboxes for capacity | Bounces by code |
| Dead addresses | Verify the list, remove every hard bounce | Bounce report |
| Low engagement or complaints | Engaged segments only; honour unsubscribes within two days; warm alongside | Postmaster Tools, JMRP |
| Shortener links | Your own subdomain | Template analyzer |
| Automated pattern | Vary timing, mailbox and content; an AI Agent per mailbox | Placement test |
When the only fix is warming
When the records are clean, the domain is on no list, the content is fine and the mail still lands in spam, the cause is reputation, and reputation is a record of engagement over time. Warming supplies it: real two-way threads, read and kept by real mailboxes across the MailStrike network, on a 21-day ramp for a new domain and continuing after. It is the slowest fix on the list and, for a cold or burned domain, the one that works.