Appendix B: Runtime Compatibility
| Runtime | Supported | Notes |
|---|---|---|
| Cloudflare Workers | ✓ | Primary target. All features. CF bindings resolve natively. |
| Node.js 18+ | ✓ | All features except ForwardableEmailMessage input and CF-specific bindings |
| Deno | ✓ | Via npm compatibility |
| Bun | ✓ | Full support |
| Browser | Partial | parse(string) + compose only — no stream, attachment, or DO support |