Outlook/Hotmail & Gmail – Deliverability Fix‑Kit (Tutorial)

A practical, step‑by‑step playbook to diagnose, fix, and prevent blocks or junking at Microsoft (Outlook/Hotmail/Live/Office 365) and Google (Gmail/Workspace).

TL;DR – Quick Checklist

  • PTR ↔ EHLO match (reverse DNS points to the exact EHLO hostname).
  • Fresh test shows SPF pass, DKIM pass, DMARC pass; ARC + SRS enabled for forwards.
  • Microsoft: check SNDS colour (green/yellow/red) and set up JMRP.
  • Google: check Postmaster domain reputation; reduce complaints.
  • Enable per‑destination throttles for Microsoft (slow lane); ramp changes gradually.
  • Use the correct unblock path (Microsoft: sender.office.com). Gmail has no delist form; rehab reputation.

Navigation

Microsoft (Outlook/Hotmail/Live/Office 365)

1) Sign up & dashboards

How to register

  1. Log in with a Microsoft account.
  2. Add all sending IPs.
  3. Validate via messages to abuse@/postmaster@ (or designated address).
  4. Check dashboards daily during rehab.

2) What moves the needle at Microsoft

  • Lower complaint rate to <0.1%; remove complainers and stale lists.
  • Fix forwards with SRS + ARC (prevents false auth fails).
  • Keep PTR ↔ EHLO exact; trim SPF includes; publish DKIM correctly; enforce DMARC.
  • Shape traffic: lower concurrency + rate for Microsoft destinations.

3) Submit unblock (after fixes)

Use sender.office.com once remediation is complete. See the template in What to Say.

Google (Gmail/Workspace)

  • Postmaster Tools: https://postmaster.google.com/
  • Watch Domain/IP reputation, spam rate, authentication.
  • There is no delist form; improvements come from sustained good signals:
    • Send only to engaged recipients; pause or cull cold segments.
    • Keep complaint rate near 0%; smoothing of volume is critical after a spike.
    • Ensure SPF/DKIM/DMARC alignment and consistent From: domains.

What to Say / What NOT to Say (MS Unblock)

Say (concise & factual):

  • Who/what: sending IP(s), domain, EHLO.
  • When/where: exact error code/text, UTC timestamps, Message‑ID(s).
  • What you fixed: PTR/EHLO match, SPF trimmed, SPF/DKIM/DMARC pass, ARC + SRS on forwards, throttles for Microsoft, compromised accounts disabled, complaint rate now <0.1%.
  • What you want: review + delist after remediation.

Do NOT say:

  • Threats/demands/ultimatums.
  • “Whitelist us” / “mission‑critical unblock NOW”.
  • Vague “all consented” without evidence.
  • Submitting before fixes are in place.
  • Spamming multiple tickets or arguing with mail ops/devs.

Polite template:

We’re seeing bounces [code & text, e.g., SC‑004 / 550 5.7.1] on YYYY‑MM‑DD HH:MM UTC for IP 203.0.113.10 (EHLO mx1.example.com), domain example.com. Since then we have: (1) matched PTR↔EHLO, (2) verified SPF/DKIM/DMARC pass, (3) enabled ARC + SRS, (4) throttled Microsoft deliveries, (5) removed complainers; complaint rate now <0.1%. SNDS is yellow/green. Sample Message‑ID: 2025...@example.com. Please review and delist. Thank you.

Microsoft Error Codes – Quick Fixes

Use these as filter tags on the page so visitors can jump straight to their code.

  • 550 5.7.1 — Spam block

    • Root causes: high complaints, auth failures, bad reputation.
    • Fix: PTR↔EHLO match; SPF/DKIM/DMARC pass; reduce complaints; throttle; submit unblock after remediation.

  • 421 4.7.0 — Temporary throttling

    • Root causes: bursty send, reputation rebuild, greylisting.
    • Fix: per‑destination slow lane; decrease concurrency; send steady trickle.

  • SC‑001 / SC‑002 / SC‑004 — Outlook policy block

    • Root causes: IP/domain reputation or policy thresholds exceeded.
    • Fix: complete remediation; document changes; submit sender.office.com.

  • 4.7.650 — Rate limits to Outlook endpoints

    • Root causes: too many parallel connections/recipients.
    • Fix: lower concurrency, increase backoff, warm gradually.

(We will expand this glossary with exact DSN text and more codes — 5.7.57, 5.7.708, 5.1.10, 5.4.317, 5.7.15, 4.7.500 — as we collect samples.)

Prevention & Hardening

  • Forwards: always SRS + ARC.
  • Rotation: DKIM selectors; DMARC from none → quarantine → reject when stable.
  • SPF: keep lean; flatten into dedicated _spf.example.com include.
  • Hygiene: remove complainers/inactives; lock compromised accounts fast.
  • Monitoring: SNDS/JMRP/Postmaster daily/weekly; blacklist watch.
  • Discipline: predictable volumes; Microsoft throttles; avoid spikes.

Related Tutorials

  • Gmail Deliverability Playbook — Diagnose, Fix, Prevent — reputation rehab, bulk-sender rules, Postmaster graphs
    → gmail-deliverability-playbook
  • Microsoft DSN / Bounce Codes – Complete Glossary — find your exact Outlook/Hotmail NDR and the remedy
    → ms-dsn-bounce-codes

References & Credible Sources

Dashboards & Requests

Authentication & Policy

SEO/Placement

  • Section: Tutorials → Email Deliverability
  • Slug: /tutorials/deliverability/fix-outlook-gmail
  • Title: Outlook/Hotmail & Gmail Deliverability Fix‑Kit — Diagnose, Fix, Prevent
  • Meta: Step‑by‑step guide to clear Outlook/Hotmail and Gmail blocks: SNDS, JMRP, Google Postmaster, ARC/SRS, and fixes for common Microsoft error codes.
  • Tags: 550-5-7-1, 421-4-7-0, SC-001, SC-002, SC-004, 4-7-650, junk-folder, deferred, rate-limited, blocked, spam-complaints-high, forwarding-issues