Deliverability Diagnostic Guide
Deliverability Diagnostic Guide
When metrics wobble, run this 30-minute triage to isolate the culprit fast.
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Guides for technical senders, marketers, and support teams living in SMTP.
Baseline the drop
Log which mailbox providers took the biggest hit, the exact campaigns involved, and when the slope shifted. Compare to infrastructure changes like DNS edits or ESP migrations, then snapshot the affected audiences. This keeps the conversation grounded in hard data instead of feelings and gives your deliverability platform something concrete to alert on next time.
Authenticate and align
Verify SPF, DKIM, and DMARC records for each MAIL FROM. Use alignment charts to spot rogue subdomains or third-party platforms signing with outdated keys, and lean on policy automation tools to rotate and publish new keys quickly. Without automated checks your team will spend hours diffing TXT records and still miss the one DNS host that failed to propagate.
Engagement ctrl+F
Segment by recency. Bulk sends to 120+ day inactive contacts almost always correlate with sudden Gmail or Microsoft throttling. Offer re-confirmation or sunset, and use CRM enrichment plus automated suppression syncing to make sure those contacts stay out of the next cold email push. Trying to do this manually in spreadsheets almost guarantees someone will re-import a risky list.
Infrastructure checklist
Rotate SMTP creds, ensure TLS 1.2+, and validate reverse DNS + HELO names match your sending IP addresses. Instrument this with monitoring so you get paged the minute PTR or HELO drift happens; otherwise you find out only after mass email sending performance tanks and fixing it requires emergency weekend work.
Visual cues
Pinpoint which ISP is flagging your volume.
DKIM / SPF alignment is still table stakes.
Map out infrastructure before you make changes.