Thanks for sharing! A few quick questions to troubleshoot:

• Any errors or logs when calling env.SEB.send()?

• Is Email Routing fully set up and recipient verified?

• Have you tried sending a simple test email without MIME formatting?

• Which Wrangler and Email API versions are you using?

• Does Email Routing work outside the Worker?

These will help pinpoint the issue. Need help with a simple test example?