Gotchas & Troubleshooting

Critical Pitfalls

Stream Consumption (MOST COMMON)

Problem: "stream already consumed" or worker hangs

Cause: message.raw is ReadableStream - consume once only

Solution:

// ❌ WRONG
const email1 = await parser.parse(await message.raw.arrayBuffer());
const email2 = await parser.parse(await message.raw.arrayBuffer()); // FAILS

// ✅ CORRECT
const raw = await message.raw.arrayBuffer();
const email = await parser.parse(raw);

Consume message.raw immediately before any async operations.

Destination Verification

Problem: Emails not forwarding

Cause: Destination unverified

Solution: Add destination, check inbox for verification email, click link. Verify status: GET /zones/{id}/email/routing/addresses

Mail Authentication

Problem: Legitimate emails rejected

Cause: Missing SPF/DKIM/DMARC on sender domain

Solution: Configure sender DNS:

example.com. IN TXT "v=spf1 include:_spf.example.com ~all"
selector._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=..."
_dmarc.example.com. IN TXT "v=DMARC1; p=quarantine"

Envelope vs Header

Problem: Filtering on wrong address

Solution:

// Routing/auth: envelope
if (message.from === "trusted@example.com") { }

// Display: headers
const display = message.headers.get("from");

SendEmail Limits

Common Errors

CPU Time Exceeded

Cause: Heavy parsing, large emails

Solution:

const size = parseInt(message.headers.get("content-length") || "0") / 1024 / 1024;
if (size > 20) {
  message.setReject("Too large");
  return;
}

ctx.waitUntil(expensiveWork());
await message.forward("dest@example.com");

Rule Not Triggering

Causes: Priority conflict, matcher error, catch-all override

Solution: Check priority (lower=first), verify exact match, confirm destination verified

Undefined Property

Cause: Missing header

Solution:

// ❌ WRONG
const subj = message.headers.get("subject").toLowerCase();

// ✅ CORRECT
const subj = message.headers.get("subject")?.toLowerCase() || "";

Limits

Debugging

Local

npx wrangler dev

curl -X POST 'http://localhost:8787/__email' \\
  --header 'content-type: message/rfc822' \\
  --data 'From: test@example.com
To: you@yourdomain.com
Subject: Test

Body'

Production

npx wrangler tail

Pattern

  async email(message, env, ctx) {
    try {
      console.log("From:", message.from);
      await process(message, env);
    } catch (err) {
      console.error(err);
      message.setReject(err.message);
    }
  }
} satisfies ExportedHandler;

Auth Troubleshooting

Check Status

const auth = message.headers.get("authentication-results") || "";
console.log({
  spf: auth.includes("spf=pass"),
  dkim: auth.includes("dkim=pass"),
  dmarc: auth.includes("dmarc=pass")
});

if (!auth.includes("pass")) {
  message.setReject("Failed auth");
  return;
}

SPF Issues

Causes: Forwarding breaks SPF, too many lookups (>10), missing includes

Solution:

; ✅ Good
example.com. IN TXT "v=spf1 include:_spf.google.com ~all"

; ❌ Bad - too many
example.com. IN TXT "v=spf1 include:a.com include:b.com ... ~all"

DMARC Alignment

Cause: From domain must match SPF/DKIM domain

Best Practices

1. Consume message.raw immediately
2. Verify destinations
3. Handle missing headers (?.)
4. Use envelope for routing
5. Check spam scores
6. Test locally first
7. Use ctx.waitUntil for background work
8. Size-check early