Cold Email Deliverability Collapsed: The Step-by-Step Triage Checklist
Total deliverability collapse across all campaigns needs a different response than a single domain issue. Here's the systematic triage process.
When deliverability collapses across multiple campaigns simultaneously, the cause is usually something systemic — a shared IP issue, an ESP change, a widespread DNS problem, or something affecting your entire infrastructure. Here's how to triage it systematically.
First 15 minutes: scope the problem
Is it one domain or all domains?
Run placement tests on 3–5 different sending domains. If only one domain is failing — it's a domain-specific issue. If multiple domains are failing simultaneously — it's systemic.
Is it a provider-specific issue?
Run placement tests and note which email provider is failing. Is it only Gmail? Only Outlook? Both? Provider-specific failure may indicate a blacklisting with that provider's network specifically.
When did it start?
Check your open rate data going back 2–4 weeks. When exactly did things start declining? What changed around that time — new ESP tool, new lists, new clients, DNS changes, warmup tool changes? The timing is often the clue.
15–30 minutes: run the full diagnostic stack
Authentication — all affected domains
Check SPF, DKIM, and DMARC on every affected domain. A systemic auth failure (e.g., your ESP rotated DKIM keys across all customers) would affect all domains simultaneously and explain a collapse. Use the DKIM checker for each domain.
Blacklist check — domains and IPs
Check your sending domains and sending IPs. If multiple IPs from your ESP are blacklisted simultaneously, it could be an ESP-level problem rather than your domain's issue specifically. Run the blacklist check on both domain and IP for each setup.
Tracking domain check — all tracking domains
Has your tracking domain's CNAME been modified, had SSL expire, or started being proxied? A tracking domain issue can affect delivery across every campaign using that tracking setup. Check with the tracking domain checker.
30–60 minutes: identify the root cause
ESP change
Contact your ESP support. Ask if they've made any infrastructure changes in the last 2 weeks — IP pool changes, DKIM key rotation, sending limit policy changes. This is a common cause of synchronized cross-domain failures.
List source quality change
Did you add a new list source recently? A new client with a poor-quality list? A purchased list? High bounce rates or spam complaints from a new source can damage multiple inboxes simultaneously if those inboxes all sent to the bad list.
Sending tool change
Did you change your sending tool or warmup tool? New tools sometimes have different IP pools with existing reputation issues.
60+ minutes: triage and assign
Classify each affected domain:
- Technical fix needed (auth, tracking) — assign fix immediately
- ESP-level issue — engage ESP support
- Reputation damage recoverable — pause and begin recovery
- Replacement needed — begin replacement process
Communication during triage
If clients are actively expecting campaign sends during triage:
- Send a brief status message within 2 hours of detection
- Don't promise resolution timelines you can't guarantee
- Pause campaign sends until root cause is identified
- Move to backup infrastructure if available
Systemic deliverability triage checklist
- Test 3+ domains to confirm scope (single vs systemic)
- Note which providers are failing (Gmail, Outlook, or both)
- Identify when decline started and what changed
- Check DKIM on all affected domains
- Check SPF on all affected domains
- Check blacklists on domains and IPs
- Check tracking domain status
- Contact ESP support about infrastructure changes
- Classify each domain: fix / recover / replace
- Move to backup infrastructure if available
- Send client status update within 2 hours
Run the checks first
Before replacing anything, run a free inbox placement test. You might find the issue is DNS, not the domain — and save yourself a week of unnecessary work.