Email Sending: lowercase info@ZONE rejected with 10202, uppercase INFO@ZONE succeeds

[ielyas]

What versions & operating system are you using?

System:
  OS: macOS 27.0
  CPU: (15) arm64 Apple M5 Pro
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 26.5.0
  npm: 11.17.0
Wrangler: 4.118.0
@cloudflare/workers-types: 5.20260731.1

Also reproducible via the Email Sending REST API path that Wrangler calls (POST /accounts/{account_id}/email/sending/send). This may be an Email Service platform bug rather than Wrangler itself — filing here because Wrangler surfaces the error and the CLI is the easiest repro.

Please provide a link to a minimal reproduction

https://gist.github.com/ielyas/5d8755da7497db2d8c1bd7b8ae35beac

Describe the Bug

Steps to reproduce

1. Onboard an apex zone to Cloudflare Email Sending (ours: ni.sa; MX remains Google Workspace; _dmarc is p=reject as added by onboarding).
2. Send with Wrangler from an allowed sender on that zone to info@ZONE:

npx wrangler email sending send \
  --from "no-reply@ni.sa" \
  --to "info@ni.sa" \
  --subject "probe" \
  --text "probe"

3. Repeat with --to "INFO@ni.sa" (same mailbox on Google Workspace).
4. Repeat with other local-parts on the same zone (contact@, elyas@, abuse@, info@updates.ni.sa on a sending subdomain, etc.).

Actual behavior

• info@ni.sa → fails with email.sending.error.email.invalid [code: 10202]
• info+tag@ni.sa → same failure
• INFO@ni.sa / Info@Ni.Sa → succeeds (CLI reports delivered)
• Other @ni.sa local-parts we tried → succeed
• info@updates.ni.sa (subdomain also onboarded for sending) → succeeds

The same failure happens from a Worker send_email binding:

await env.EMAIL.send({
  to: "info@ni.sa", // fails
  from: { email: "no-reply@ni.sa", name: "Website Contact Form" },
  replyTo: "user@example.com",
  subject: "Contact Form",
  text: "...",
});

Using to: "INFO@ni.sa" works around it. Account + zone suppression lists were empty (GET .../email/sending/suppression → total: 0).

Expected behavior

Recipient addresses should be treated case-insensitively (or at least info@ZONE should not be uniquely rejected when INFO@ZONE and other local-parts work). Docs (llms-full.txt / error table) describe 10202 as “Invalid email content,” which does not explain a case-sensitive local-part rejection, and examples freely use info@… addresses.

Happy to provide account/zone IDs privately if useful.

Please provide any relevant error logs

✘ [ERROR] A request to the Cloudflare API (/accounts/.../email/sending/send) failed.

  email.sending.error.email.invalid [code: 10202]

From https://developers.cloudflare.com/email-service/api/send-emails/rest-api/ :

HTTP	Code	Message	Description
400	10202	email.sending.error.email.invalid	Invalid email content

Workers binding throws into our catch path as a delivery failure (no distinct string code surfaced in our logs beyond the send failing).

[workers-devprod]

Note

This is an automated, advisory triage report generated by workers-devprod. It is not an official maintainer response — a maintainer will follow up.

🤖 Automated triage report

Issue Triage: #65

Summary

Sending email to info@ni.sa via wrangler email sending send (and the send_email Worker binding) is rejected by the Cloudflare Email Service API with email.sending.error.email.invalid [code: 10202], while the same mailbox addressed as INFO@ni.sa and other local-parts on the same zone succeed.

Classification

• Type: Bug
• Component: packages/wrangler (surfaces the error) — but root cause is the Cloudflare Email Service API, not workers-sdk
• Severity: Medium
• Has Reproduction: Yes (gist + step-by-step CLI repro): https://gist.github.com/ielyas/5d8755da7497db2d8c1bd7b8ae35beac
• Quality: Complete

Findings

• Created: 2026-07-31
• Author: ielyas
• Version: Wrangler 4.118.0, @cloudflare/workers-types 5.20260731.1, Node 26.5.0, npm 11.17.0, macOS 27.0 (arm64)
• Labels: none
• Comments: 0

Analysis

• The failure is returned by the Cloudflare API (POST /accounts/{account_id}/email/sending/send) with error code 10202. Wrangler and the send_email binding both merely surface this API error — the reporter confirms it reproduces on the raw REST path independent of Wrangler.
• Root cause therefore lies in the Email Service platform, not in workers-sdk. There is no tooling fix available in packages/wrangler; the CLI is correctly passing the address through and reporting the API's rejection.
• The behavior itself looks like a genuine platform bug: a specific lowercase local-part (info@ZONE, info+tag@ZONE) is uniquely rejected while INFO@ZONE, other local-parts, and the subdomain variant all succeed. Case-sensitive rejection of a recipient local-part is not expected behavior.
• The 10202 error string ("Invalid email content") is also misleading for this scenario — it does not describe a case-sensitive local-part rejection, which is a secondary error-messaging concern.
• Issue is well-documented: clear repro steps, matrix of what fails vs. succeeds, version/OS info, error logs, and reference to the docs error table. No missing information.
• Brand-new issue (created and last updated same day), so not stale; no duplicate reference present.

Recommendation

Status: NEEDS VERIFICATION

Reasoning: The error originates from the Cloudflare Email Service API (code 10202), not from Wrangler — the reporter confirmed it reproduces on the raw REST endpoint and the send_email binding. This is a platform/API validation issue that cannot be fixed within workers-sdk, so it should be verified and routed to the Email Service team rather than fixed in the CLI.

Action: Confirm the behavior against the Email Service API directly, then route/escalate to the Cloudflare Email Service platform team (the issue may need to be tracked internally rather than in workers-sdk). If maintainers decide the CLI should improve how it surfaces the 10202 error, that is a separate, minor tooling follow-up.

Suggested Labels: (none — omitted; do not guess at labels that may not exist in the repo)

Suggested Comment

Thanks for the detailed report and repro. Based on what you've described, this rejection is coming from the Cloudflare Email Service API itself (the 10202 error on POST /accounts/{account_id}/email/sending/send), not from Wrangler — Wrangler and the send_email binding are just surfacing the API's response, which is also why it reproduces on the raw REST path.

That means we can't fix the underlying case-sensitive rejection in workers-sdk; it needs to go to the Email Service platform team. Could a maintainer help verify this against the API and route it to the Email Service team? The offer to share account/zone IDs privately is appreciated and will likely be needed for them to investigate.

If it turns out there's also something Wrangler should do differently in how it presents the 10202 error, we can track that separately here.

Structured summary (JSON)

{
  "issueNumber": 14957,
  "title": "Email Sending: lowercase info@ZONE rejected with 10202, uppercase INFO@ZONE succeeds",
  "githubUrl": "https://github.com/cloudflare/cf-platform-issues/issues/65",
  "recommendation": "NEEDS VERIFICATION",
  "difficulty": "n/a",
  "reasoning": "The rejection comes from the Cloudflare Email Service API (code 10202), not from Wrangler, and reproduces on the raw REST path and the send_email binding. It cannot be fixed within workers-sdk and needs verification and routing to the Email Service platform team.",
  "suggestedAction": "Verify the behavior against the Email Service API and route/escalate to the Cloudflare Email Service platform team; any change to how Wrangler surfaces the 10202 error would be a separate minor tooling follow-up.",
  "hasSuggestedComment": true,
  "suggestedLabels": []
}