Mailgun Inspect — Email Preview & Testing for VS Code

Preview your HTML emails across 100+ email clients and run full content analysis — accessibility, spam, link, and image checks — without leaving VS Code.

Get started in 3 steps

Create a Mailgun account — 30-day free trial, no credit card required
Install this extension and open a .html email file in VS Code
Click the Mailgun Inspect icon in the title bar → New Test → select email clients

The icon opens a Recent Tests page with the latest 10 tests created on or after October 1, 2026 at 00:00 UTC, newest first, from your API key's account and configured US or EU region. Older v2 tests are excluded; this extension reads v3 results only. Click a test to reopen its active version's saved previews and checks, or click Refresh to reload the list.

New Test always prompts for email clients, with any configured defaults preselected, and tests the HTML file shown on the page. Canceling client selection does not create a test. Existing tests are read without creating a new test or rerunning checks; source-line navigation is disabled because saved tests are not associated with a local file.

The results panel includes View full results in Mailgun, which opens the saved test in your browser using your configured US or EU region. Sign in to the Mailgun account used to create the test to view its full results.

What you can test

Rendering — 100+ clients including Gmail, Outlook, Apple Mail, and dark mode variants

Accessibility — 45+ WCAG 2.2 checks for EAA compliance

Code analysis — 38+ HTML/CSS compatibility issues detected automatically

Link validation — broken URLs and redirect chains caught before you send

Image validation — missing alt text, broken sources, oversized images

The Links and Images badges count items with validation issues, including warnings on otherwise valid URLs (such as an SSL certificate expiring soon). All reported findings are displayed for each affected link or image.

Spam testing — B2B and B2C spam filter analysis from neutral IPs

Some content checks require an entitled Mailgun plan. If a check is not available on your account, the corresponding tab will indicate that the feature is not enabled.

Closing or replacing the results panel cancels its outstanding requests and polling. Requests time out after 30 seconds. Transient polling failures retry up to three consecutive attempts with backoff and respect the API's retry guidance; authentication, missing-resource, and malformed-response errors stop the affected checks. Generate a new preview to retry a stopped test.

Requirements

VS Code 1.85+
Mailgun account with Inspect access (start free)
API key (set via Command Palette → "Mailgun Inspect: Set API Key")

FAQ

Do I need a paid account? A Mailgun Inspect subscription is required — 30-day free trial available, no credit card needed.

Which clients are supported? 100+ including all Outlook versions, Gmail, Apple Mail, iOS, Android, Samsung Mail, and dark mode.

Can I use MJML or React Email? Current version supports .html files. MJML and React Email support is on the roadmap.

Support

Privacy

The extension sends the HTML of the active editor to the Mailgun Inspect API for rendering and analysis. No content leaves your machine until you explicitly trigger a preview. No background activity. Covered by SOC 2 · HIPAA · GDPR · ISO 27001.

Use of Sinch Services

This extension provides developers with a way to interact with Sinch APIs and services from supported developer tools or environments. Use of Sinch services requires a valid Sinch account and is subject to the applicable Sinch Terms of Service available at: Explore Terms of Service - Sinch

This extension may be used in conjunction with third-party developer tools, IDEs, platforms, or environments that are not operated or controlled by Sinch. Such third-party tools or platforms are subject to their own terms and policies. The extension is provided on an "as-is" basis, and Sinch is not responsible for the operation, availability, performance, or security of any third-party tools or platforms.

Telemetry

Sinch's Mailgun Inspect VS Code Extension may collect limited telemetry data to help us understand usage and improve the extension's experience. The extension does not collect any personal data or any message content. Telemetry collection follows the user's global telemetry setting in Visual Studio Code and will be disabled if telemetry is turned off in VS Code settings.

Development

Use Node.js 22, run npm ci, then npm run check to run ESLint, a clean TypeScript build, and the regression suite. Tests exercise the API transport, check controller, recent-test history, webview DOM, and command-to-panel flow using mocked VS Code and API services; they do not require credentials or send email content to Mailgun.

Press F5 in VS Code to run the extension in an Extension Development Host. Before releasing, smoke-test real previews in both regions, source navigation, spam dispatch, panel closure, and the Mailgun browser link.

npm run compile removes stale output before rebuilding. Package with npx @vscode/vsce package; the VSIX allowlist includes only the manifest, readme, image assets, and compiled extension code. CI runs the checks and an npm dependency audit.