Goals

Allow users to configure which email clients they want to see compatibility warnings for in the preview server.

Background

When developing emails for enterprise/corporate environments (especially airgapped networks), the target email client is often exclusively Microsoft Outlook. In these scenarios, warnings about Yahoo Mail, Gmail, Apple Mail, etc. are noise that clutters the development experience.

Currently, the compatibility checker shows warnings for all email clients with no way to filter them.

Proposal

Add a configuration option to filter which email clients to show warnings for. This could be:

Option 1: CLI flag

email dev --clients outlook,outlook-legacy
# or inverse
email dev --ignore-clients yahoo,gmail,apple-mail

Option 2: Config file (react-email.config.js)

export default {
  compatibility: {
    // Only show warnings for these clients
    clients: ['outlook', 'outlook-legacy', 'outlook-web'],
    // Or ignore specific clients
    // ignoreClients: ['yahoo-mail', 'gmail']
  }
}

Option 3: Per-template configuration

TestEmail.compatibilityClients = ['outlook', 'outlook-legacy'];

Use Case

• Enterprise environments with standardized email clients
• Military/government airgapped networks using only Outlook
• B2B applications where target audience uses specific email clients
• Reducing noise during development to focus on relevant issues

Additional Context

The compatibility data comes from Can I Email, which already categorizes by email client, so filtering should be straightforward to implement.