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 six causes, how to confirm each, and the fix
Confirm it: Bounces and complaints in the days after the send: the sequencer's bounce report by code, the spam rate in Postmaster Tools, JMRP complaints at Outlook.com.
Fix it: Remove every hard bounce and every address without recent engagement, cut the volume back to the engaged segment, and keep it there until placement recovers. Bounce rate guide.
Confirm it: Sent volume by day against the week before, and Google's 421 4.7.28 (unusual rate of unsolicited mail) or 550 5.7.1 rate-limited in the bounces.
Fix it: Return the volume to the curve it was on and climb from there; add warmed mailboxes for capacity rather than pushing one. Safe volume by domain age.
Confirm it: A new template, a new tracking or link domain, an attachment, an image-only body. Score the message and check the domains it links to.
Fix it: Move tracking to a subdomain you own, link only to domains you would send from, write one message for one person. Template analyzer.
Confirm it: A new rejection code in the bounces (550 5.7.26 at Gmail since November 2025, 550 5.7.515 at Outlook.com since May 2025), or a DNS change that broke alignment.
Fix it: SPF, DKIM and aligned DMARC on the domain and every service sending for it, confirmed on a real message's headers. Compliance checker.
Confirm it: The sending domain or mailbox is under 30 days old, or outreach started on it before any warmup.
Fix it: Stop the outreach, run the 21-day ramp, test placement at the end. How long warmup takes.
Confirm it: The spam rate in Postmaster Tools climbing toward Google's 0.10% and 0.30% lines; JMRP reports at Outlook.com; a segment or a campaign that drew them.
Fix it: Stop the segment, honor every unsubscribe within two days, and rebuild with mail people asked for. Past 0.30%, Google needs seven consecutive days below it before mitigation. Postmaster recovery steps.
The twenty-minute checklist
- 1
Placement, per provider (5 minutes)
Send the same message to mailboxes you control at Gmail, Outlook.com and a Microsoft 365 tenant, or run the Free Deliverability Test. Spam everywhere is the sender; spam at one provider is that provider's record of you.
- 2
The bounces, by code (5 minutes)
Open the sequencer's bounce report and read the codes, not the count. 5.7.26 and 5.7.515 are authentication; 4.7.28 is volume; 5.1.1 is the list; 5.7.1 low reputation is the record.
- 3
Authentication and alignment (5 minutes)
The auth checker on the domain, then on a message's headers. A platform signing with its own domain is the change nobody remembers making.
- 4
The consoles (5 minutes)
Postmaster Tools for the spam rate and the tier; SNDS for the IPs at Outlook.com. Then the public record in the reputation checker: blacklists, PTR, domain age.
- Google Workspace emails going to spam: the Postmaster-led diagnosis.
- Microsoft 365 emails going to junk: headers, Message Trace, Quarantine, SNDS.
- Why emails go to spam: the ten causes when it was never landing well.
Questions about a sudden drop
Why are my emails going to spam all of a sudden?
Because something changed in the week before: a list import that produced bounces and complaints, a jump in volume, new content or a new tracking domain, a provider rule that started biting (Gmail's and Microsoft's authentication rejections), a new domain sending before it was warmed, or a rise in complaints. Each leaves a different trace, and the sections above say where to look for each.
Why are my emails going to junk mail all of a sudden in Outlook?
The same six causes, and at Microsoft the first one to rule out is authentication: since 5 May 2025 Outlook.com rejects high-volume mail that fails SPF, DKIM or aligned DMARC, and a Microsoft 365 tenant can quarantine or reject on a DMARC failure at any volume. Read the anti-spam headers on a junked message; the Microsoft 365 page walks the trace.
My new domain's emails are going to spam. Is that normal?
Yes, and it is the one cause on this page that is not a change on your side: a domain under 30 days old has no history, and the receivers filter it on caution regardless of its records. Outreach waits for the 21-day ramp, and a placement test at the end shows when the providers trust it.
How long does it take to recover from a sudden drop?
It depends on the cause. A broken record is fixed the day DNS propagates; a volume jump recovers when the volume returns to its curve; a spam-rate problem needs the rate to fall and, at Google, seven consecutive days below 0.30% before mitigation; a reputation drop needs the engagement record rebuilt, which takes weeks rather than days.
Should I switch domains after a sudden drop?
Not first. A new domain starts with no history and a 21-day ramp, and the cause that hit the old domain hits the new one on the first send. Find the change, fix it, and rebuild; a new domain is for a domain that is blacklisted or burned beyond recovery.