Add Provider Adapters
Added first-party email provider adapters for Resend, SendGrid, Postmark, and Mailgun. These adapters send directly with fetch, support the shared sendEmail() flow, and map provider responses into SendEmailReceipt.
Add Email Layout Helpers
Added email-safe layout and content primitives including Box, Card, Flex, Grid, Spacer, List, ListItem, CodeInline, CodeBlock, ColorScheme, and Conditional. Flex and Grid render table-based layouts for email client compatibility, and Outlook conditional comments remain covered by strict validation.
Build and Plugin Updates
Migrated the build to tsdown, added provider entry points, and changed the Tailwind plugin package to named exports such as vitePlugin, webpackPlugin, and EmailTailwindUnplugin.