Diagnosis order — 1) Check DNS health for the domain (drift is the most common cause). 2) Check blocklist status. 3) Confirm you haven't scaled cold sending above what the warming supports. 4) Check the spam rate trend for the same period. Each of these has a specific fix.
Diagnosis by cause
1. DNS drift (most common)
Someone or something changed a DNS record at your registrar. SPF, DKIM, or DMARC no longer verifies.
- Check the Domains page for the affected domain's health indicator. Yellow or red = DNS issue.
- Click into the domain, review each record.
- Fix per DNS verification failing.
2. Blocklist listing
The domain got listed on Spamhaus, SURBL, or another blocklist.
- Check domain detail panel's blocklist shield.
- If listed, see Domain on blocklist for delisting.
- Health won't recover until the listing is resolved.
3. Cold sending outpaced warming
You started sending real cold campaigns at high volume before the mailbox was ready. Providers noticed the spike and started filtering more aggressively.
- Check your sending volume for the past 7 days at the mailbox level.
- If it's above 25-40 cold emails/day and the mailbox is under health 85, you're pushing too hard.
- Scale back cold volume to 10-15/day and let warming continue for another week.
4. Content triggers
Recipients are marking your cold campaigns as spam. Spam rate rises, which drags health.
- Check the warming metrics' spam rate trend. Rising spam rate matches the health drop.
- Review your recent cold campaign content — spammy subject lines, weak targeting, obvious bulk send patterns.
- Fix the content, don't just wait — reputation compounds until you address the root cause.
5. Provider-side changes
Rare but happens. Gmail or Microsoft occasionally tightens spam filtering globally. Fleet-wide drops without any other explanation may be provider-driven.
- Check social media (r/EmailForensics on Reddit is a good source) for reports.
- If it's a global provider change, ride it out — usually normalizes in a week.
Prevent future drops
- Monitor DNS health weekly. Catch drift before it drops warming.
- Ramp cold sending gradually. Don't jump from warming volume to full cold volume overnight.
- Watch spam rate as a leading indicator. Rising spam predicts a health drop before it happens.
What's next
Frequently asked questions
How much drop is worrying?
5 points in a day = normal noise. 10+ points in a day = something changed. 20+ points overnight = active problem, investigate immediately.
What if all my mailboxes on a domain dropped at the same time?
Domain-level cause — DNS drift or blocklist listing. Individual mailbox issues affect only one mailbox, not the whole domain.
What if the drop is fleet-wide across all domains?
Rarer, but possible. Usually means either a Winnr platform issue (contact support to confirm), or your list quality has cratered and you're getting spam complaints across the fleet.
My inbox rate is still fine but health dropped. What?
Health tracks the spam rate directly (health = 100 − 2 × spam rate), and inbox rate is the exact complement of spam rate — so a real health drop should move inbox rate with it. If they look out of sync, you're probably comparing different time windows (health uses recent sends). Recheck both over the same period; a genuine drop means spam placement rose.
Should I pause warming while diagnosing?
Only for domain-level issues where you suspect ongoing damage (blocklist, DNS drift). For individual mailbox issues, keep warming running while you diagnose.