Pick the diagnostic that matches the question
Use narrow public tools for one DNS, header, or policy question. Use the full deliverability tester when the problem spans authentication, content, routing, links, and sender reputation.
Tools
Tools & operations
Reading the WillItInbox report, API integration, CI/CD workflows, and the operational craft of running mail.
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.
Explore free email toolsRun bounded MX, SPF, DMARC, MTA-STS, and header diagnostics before moving into monitored product workflows.
Curated guide
Turn one report into an operating workflow
A single report is useful; repeated checks become operational leverage when they are connected to release reviews, regression tests, webhooks, and team-visible evidence.
Automate what repeats
API, SDK, and webhook workflows are the right fit when validation, monitoring, and deliverability checks need to run inside product flows or release pipelines without manual copy-paste.
Diagnostic workflow
- Step 1
Choose the smallest diagnostic
Start with the free check that matches the current DNS, policy, or header question.
Open workflow - Step 2
Run the complete workflow
Use message testing, validation, monitoring, or placement when the job crosses multiple evidence layers.
Open workflow - Step 3
Automate repeatable checks
Use API, SDK, webhook, and CI patterns for release and operations workflows.
Open workflow
Relevant free tools
- Free tools hub
Open all five public diagnostics from one page.
- Header analyzer
Analyze up to 64 KB of headers without retaining submitted data.
Pillar guide
How to read a WillItInbox deliverability report
·3 min read
Prioritize authentication, routing, headers, content, links, and infrastructure findings without treating the score as a delivery guarantee.
Read pillarSupporting guides
- ·9 min read
SMTP vs API for Transactional Email: An Engineer's Honest Comparison
SMTP vs API for transactional email: throughput, retries, idempotency, error granularity, attachments, webhooks — plus when SMTP still wins.
Read - ·10 min read
SMTP Ports 25 vs 465 vs 587: Which One Should You Actually Use?
SMTP port 587 vs 465 vs 25 explained: relay vs submission roles, why ISPs block port 25, RFC 8314 implicit TLS, port 2525 fallback, and a decision table.
Read - ·10 min read
How to Read Email Headers: A Complete Analysis Guide
Learn how to read email headers step by step: the Received chain, Authentication-Results, ARC, X- headers, and how to trace an email's true origin IP.
Read - ·12 min read
How to Test Transactional Email in Development (Without Emailing Real
Learn how to test transactional emails safely in development using sandbox SMTP, environment isolation, and recipient allowlists — without emailing real users.
Read - ·10 min read
SMTP Error Codes Explained: 550, 551, 552, 554 (and What to Do About Each)
SMTP error codes decoded: what 550, 551, 552, and 554 bounces mean, when to retry, and when to suppress the address permanently.
Read - ·2 min read
Deliverability QA in CI/CD with the WillItInbox API
How developers can turn deliverability testing and validation into repeatable checks around releases, templates, and imports.
Read - ·3 min read
Email validation API status guide
Email validation API results explained: act on valid, invalid, risky, catch-all, and unknown statuses using 12-layer evidence and confidence scores.
Read
Frequently asked questions
- When should a free check become a monitored workflow?
- Move to monitoring when evidence must be retained, compared over time, shared with a team, or connected to alerts and remediation.
- Can the API be used in CI/CD?
- Yes. Use stable check identifiers, explicit thresholds, bounded polling or signed webhooks, and archive the report with the release.