Diagnose the full send path
A useful deliverability review starts with the exact message, sender domain, signing path, DNS, links, and receiving evidence. Single-signal checks are helpful only when they are tied back to the full route.
Deliverability
Deliverability fundamentals
Why mail lands in spam, bounce handling, list hygiene and the engagement signals that move the needle.
How to use this topic
Start with the pillar guide for the full model, follow the diagnostic workflow for the current problem, and use the commercial destination when the evidence needs to become a repeatable team process.
Run an email deliverability testSend the production-like message and inspect authentication, headers, content, links, DNS, and prioritized fixes.
Curated guide
Separate durable fixes from symptoms
Authentication failures, broken return paths, poor list hygiene, and complaint patterns deserve priority over cosmetic copy changes. The best fixes reduce repeated risk across future campaigns.
Keep measurement honest
Retest after meaningful changes, keep reports as baselines, and avoid claiming an inbox guarantee from one diagnostic. Provider behavior, engagement, and recipient history still matter.
Diagnostic workflow
- Step 1
Test the real message
Use the same sender, signer, links, MIME output, and infrastructure planned for production.
Open workflow - Step 2
Fix durable failures
Prioritize authentication, routing, and list-quality evidence before cosmetic warnings.
Open workflow - Step 3
Retest and monitor
Keep the report as a baseline and monitor the sending domain for drift.
Open workflow
Relevant free tools
- Header analyzer
Inspect message structure and unsubscribe publication with PII redaction.
- MX lookup
Confirm the receiving route and diagnose missing or conflicting MX records.
Pillar guide
Gmail and Yahoo sender requirements checklist
·5 min read
Check the Gmail and Yahoo bulk sender rules for SPF, DKIM, DMARC, one-click unsubscribe, complaint rate, TLS, PTR, and list quality before scaling.
Read pillarSupporting guides
- ·2 min read
Inbox placement testing: seed tests, limits, and repeat checks
Use seed inboxes to collect diagnostic placement samples, compare repeat tests, and avoid treating one run as a universal inbox guarantee.
Read - ·2 min read
Bulk email validation CSV checklist
A practical checklist for uploading, validating, segmenting, and exporting CSV email lists without damaging sender reputation.
Read - ·3 min read
How to check if an email will go to spam before launch
Test the final production-like message, separate durable failures from warnings, and retest the same sender path before launch.
Read - ·3 min read
Why emails land in spam: reputation, content, and list evidence
Diagnose spam-folder problems by separating sender reputation, list quality, authentication, content, links, and provider-specific evidence.
Read - ·4 min read
Bounces decoded: hard, soft, block, and how to handle each
What every SMTP bounce code actually means, which ones to retry, and the suppression rules that keep your reputation intact.
Read - ·3 min read
Feedback loops (FBLs): how to know when recipients hit 'spam'
Every major receiver's FBL program, how to enroll, and the suppression discipline that turns complaints into long-term placement gains.
Read - ·3 min read
List-Unsubscribe header setup and testing
Add List-Unsubscribe and List-Unsubscribe-Post headers, build the RFC 8058 POST endpoint, avoid common Gmail/Yahoo mistakes, and test compliance.
Read - ·2 min read
Return-Path explained: bounce handling and SPF alignment
Understand who sets the Return-Path, how it receives bounces, and when its domain must align for SPF-based DMARC authentication.
Read - ·4 min read
Email list hygiene: suppress, sunset, or remove
Build a list-hygiene policy for invalid, inactive, risky, and unengaged recipients without confusing validation with consent.
Read - ·2 min read
Transactional vs marketing email — separate them or suffer
Why running both streams from the same domain is a deliverability liability and how to split them cleanly.
Read
Frequently asked questions
- Can a deliverability test guarantee inbox placement?
- No. It provides technical and diagnostic evidence; reputation, engagement, recipient history, and provider behavior also affect placement.
- What message should be tested?
- Test the final production-like message after tracking, personalization, footer injection, and ESP rewriting are enabled.