Gmail Deliverability Playbook — Diagnose, Fix, Prevent

A practical, step‑by‑step guide to recover and harden Gmail/Google Workspace deliverability. Use this with the Outlook/Hotmail Fix‑Kit and Microsoft DSN Glossary.

TL;DR — Quick Checklist

  • Authenticate & align: SPF pass, DKIM pass, DMARC pass with aligned From domain.
  • Meet bulk‑sender rules (2024+): DMARC published (at least p=none), one‑click List‑Unsubscribe, low spam rate.
  • Reputation first: Check Google Postmaster Tools domain & IP reputation; stop risky sends if reputation is bad/low.
  • Send to engaged only: Pause cold/unengaged segments; reduce volume and smooth cadence.
  • Consistency: Keep From: domain, DKIM d= domain, and sending IPs stable during rehab.
  • Content & links: Avoid spammy patterns; use reputable URLs; don’t mix many unrelated links.

Postmaster Tools — Setup & What to Watch

URL: https://postmaster.google.com/

Setup

  1. Log in with a Google account.
  2. Add your sending domain.
  3. Verify ownership with the provided DNS TXT.

Dashboards to watch

  • Domain reputation / IP reputation: aim for Medium/High. If Low/Bad, cut volume and fix root causes.
  • Spam rate: keep as close to 0% as possible; spikes precede junking.
  • Authentication: verify SPF/DKIM/DMARC pass and alignment trends.
  • Delivery errors: look for patterns (deferrals, rate‑limits) during spikes.

Tip: Postmaster trends lag — hold a clean pattern for several days to see improvements reflected.

Gmail Bulk‑Sender Requirements (2024+)

  • SPF & DKIM: mail must pass at least one, and
  • DMARC: publish a policy (at least p=none) for your From domain.
  • One‑Click Unsubscribe: include both headers on promotional mail:
    List-Unsubscribe: <mailto:unsubscribe@example.com>, <https://example.com/u/12345>
List-Unsubscribe-Post: List-Unsubscribe=One-Click
  • Low spam rate: keep spam complaints extremely low (use engagement filtering; remove complainers promptly).
  • Valid PTR (rDNS): EHLO hostname must match PTR.
  • TLS: always send with TLS; keep certs valid and chain complete.

If you send 5000+ messages/day to Gmail, treat all of the above as mandatory. Even below that, following them helps inboxing.

Reputation Rehab Plan (7–14 days)

Day 0–1: Triage & Fixes

  • Fix alignment: SPF, DKIM (correct selector and d=), DMARC alignment with From:.
  • Ensure consistent From domain and DKIM d=; don’t rotate during rehab.
  • Add one‑click unsubscribe headers on bulk mail.
  • Pause all cold/unverified lists; send only to users active in last 30–90 days.
  • Cut volume to 20–40% of normal; smooth cadence (no spikes).

Day 2–7: Controlled sending

  • Send only high‑engagement segments (recent opens/clicks/replies).
  • Throttle sends; avoid large, sudden batches.
  • Watch Postmaster Domain/IP reputation daily; keep spam rate ~0%.

Day 8–14: Gradual ramp

  • If reputation improves to Medium/High, slowly increase volume.
  • If reputation stays Low/Bad, keep volume reduced and re‑audit: content, list sources, bounces, forwarding behavior.

Common Gmail Responses — Symptoms & Fixes

Gmail’s NDRs are less standardized than Microsoft’s. Focus on reputation, alignment, and engagement. When in doubt, reduce volume and improve signals.

  • Authentication/Alignment failures (mentions of SPF/DKIM/DMARC failing or misaligned)

    • Fix: Ensure SPF covers the sending IP; DKIM signs with a stable d= aligned to From:; DMARC uses the same organizational domain.

  • “Message rejected for spam” / points to Gmail support pages

    • Fix: Remove risky content/links; send to engaged recipients only; let reputation recover before ramping.

  • Deferrals / temporary failures (retry later)

    • Fix: Lower concurrency and rate; spread sends over time; keep retry windows reasonable; monitor for improvement.

  • Blocks after a spike

    • Fix: Stop bulk for 24–48h; resume with small, engaged cohorts; maintain alignment; avoid content changes that look “new”.

Alignment Details (quick reference)

  • SPF: include the exact sending hosts; keep records under 10 DNS lookups; use a dedicated include like _spf.example.com if you flatten.
  • DKIM: use a stable selector and d= domain; ensure public key DNS is correct and not split incorrectly; sign headers consistently (From, Subject, Date, Message‑ID).
  • DMARC: publish at least p=none while rehabbing; move to quarantine/reject when stable; ensure alignment (relaxed or strict) matches your setup.
  • ARC (optional but helpful on forwards): preserves authentication results across forwarding; useful if your users forward mail.

Content & List Hygiene

  • Unsubscribe clarity: visible in body + one‑click headers to reduce “Report spam”.
  • Predictable sending identity: keep From: name, domain, and IPs stable.
  • Link reputation: avoid link shorteners; use HTTPS; limit third‑party trackers.
  • List sources: confirm opt‑ins; remove role accounts and long‑inactive addresses.
  • Bounce handling: hard bounces removed immediately; soft bounces limited retries.

Verify via Headers (spot‑check)

Look for Authentication-Results: from mx.google.com, e.g.:

Authentication-Results: mx.google.com;
    spf=pass (google.com: domain of bounce@example.com designates 203.0.113.10 as permitted sender) smtp.mailfrom=bounce@example.com;
    dkim=pass header.d=example.com header.s=dkim2025 header.b=…;
    dmarc=pass (p=none sp=none) header.from=example.com
  • Pass/pass/pass + improving Postmaster reputation ⇒ you’re on the right track.

Related Tutorials

References & Further Reading

If you keep seeing rejections/deferrals after following this playbook, capture full SMTP transcripts and headers and review Postmaster graphs. Then adjust volume and targeting until reputation improves.