workerd error: email binding send failed

workerd error: email binding send failed

TL;DR

The email binding's send failed: check the binding config, the sender address (must be verified), and the message (size, recipients). Then check the Email Routing / MailChannels status. The binding is a thin wrapper; the failure is usually config or content.

workerd error: email binding send failed

Steps

1. Verify the binding is configured and the sender address is verified for the domain. Expected: The sender is legitimate.

2. Check the message: size limits, recipient count, valid addresses. Expected: The content fits the limits.

3. Test with a minimal send to isolate config vs content. Expected: The failing half is identified.

4. Check the provider status (MailChannels / Email Routing) for outages. Expected: External issues are ruled out.

5. Log send failures with the error detail for alerting. Expected: Failures are visible.

When to use

• the Workers email binding fails to send
• setting up email sending
• sends worked before

When not to use

• not using the email binding (different sending path)
• the error is on receive (Email Routing, different config)
• the recipient rejects (check the bounce, not the binding)

Tool compatibility

• workerd
• Email bindings

Variant phrasings

• "workerd email binding send failed"
• "workers email send failed"
• "email binding cloudflare error"

Why it happens

The email binding wraps a sending provider with strict requirements: verified senders, size limits, recipient limits. Most failures are the sender not being verified or the message exceeding limits. The binding surfaces the provider's error; reading it points at the fix.

Edge cases

• sender verification is per-domain; check the exact domain
• the binding is for transactional mail, not bulk; volume limits apply
• DMARC alignment affects deliverability, not just sending

Provenance

Resolved from the public thread: https://vectle.com/posts/pstEAMeChNQoKJKDBfdWfvOQ

Resolved from the public thread: https://vectle.com/posts/pstEAMeChNQoKJKDBfdWfvOQ

Thread query: workerd error: email binding send failed

TL;DR: The email binding's send failed: check the binding config, the sender address (must be verified), and the message (size, recipients). Then check the Email Routing / MailChannels status. The binding is a thin wrapper; the failure is usually config or content.