email-send

---

title: email.send

description: Send transactional emails through Resend.

keywords: [helmdeck, email, email.send, resend, MCP]

---

email.send

email.send sends transactional emails through Resend using a Vault-managed API key. Agents typically use this pack for notifications, password resets, onboarding emails, verification links, or workflow-driven outbound communication. The pack validates required fields, verifies that the sender domain is registered and verified on Resend, submits the email through the Resend API, and returns the resulting message ID.

Inputs

Field	Type	Required	Default	Notes
from	string	yes	—	Sender email address. The domain must already be verified on Resend.
to	string	yes	—	Recipient email address.
subject	string	yes	—	Email subject line.
html	string	no	—	HTML email body.
cc	string	no	—	Optional CC recipient.
bcc	string	no	—	Optional BCC recipient.
reply_to	string	no	—	Optional reply-to address.

Outputs

Field	Type	Notes
id	string	Resend-generated message ID for the submitted email.

Vault credentials needed

• resend-api-key — type api_key, scoped to host pattern *. Add via the Management UI's Vault panel before invoking. If absent, the pack fails with invalid_input.

Use it from your agent (OpenClaw chat-UI worked example)

User: Send a welcome email to user@example.com from hello@example.com.

Tool used:

{
  "pack": "email.send",
  "input": {
    "from": "hello@example.com",
    "to": "user@example.com",
    "subject": "Welcome!",
    "html": "<h1>Welcome to Helmdeck</h1><p>We're glad you're here.</p>"
  }
}

Agent reply:

Sent the welcome email successfully. Resend accepted the message for delivery and returned a message ID for tracking.

Verified via OpenClaw + helmdeck on 2026-05-22.

Developer reference (curl)

For engineers wiring agent-free automations or debugging pack contracts directly. Mint a JWT first:

ADMIN_PW=$(grep HELMDECK_ADMIN_PASSWORD /root/helmdeck/deploy/compose/.env.local | cut -d= -f2)
JWT=$(curl -fsS -X POST http://localhost:3000/api/v1/auth/login \
  -H 'Content-Type: application/json' \
  -d "{\"username\":\"admin\",\"password\":\"${ADMIN_PW}\"}" \
  | python3 -c 'import sys,json;print(json.load(sys.stdin)["token"])')

Happy path:

curl -fsS -X POST http://localhost:3000/api/v1/packs/email.send \
  -H "Authorization: Bearer $JWT" \
  -H 'Content-Type: application/json' \
  -d '{
    "from": "hello@example.com",
    "to": "user@example.com",
    "subject": "Welcome!",
    "html": "<h1>Hello</h1><p>Welcome aboard.</p>"
  }'

Real captured response:

{
  "pack": "email.send",
  "version": "v1",
  "output": {
    "id": "d91cd9bd-1176-453e-8fc1-35364d380206"
  },
  "duration_ms": 231
}

Error codes

Code	Triggers	Captured response
invalid_input	Missing required fields (to, subject)	{"error":"invalid_input","message":"subject is required"}
invalid_input	Missing Vault credential	{"error":"invalid_input","message":"vault credential \"resend-api-key\" not found"}
invalid_input	Sender domain not verified on Resend	{"error":"invalid_input","message":"cannot send email from \"hello@example.com\" because the sender domain is not verified on Resend"}
handler_failed	Upstream Resend API failure	{"error":"handler_failed","message":"unauthorized"}

The closed-set codes are defined in internal/packs/errors.go: invalid_input, invalid_output, schema_mismatch, session_unavailable, handler_failed, artifact_failed, timeout, internal.

Session chaining

• No session. Stateless; no _session_id field accepted; chains freely with anything.

Async behavior

Synchronous only.

The pack returns immediately after Resend accepts the email submission request. The returned message ID may be used later for delivery-status querying if such a companion pack is introduced.

See also

• Catalog row: docs/PACKS.md
• Source: internal/packs/builtin/email_send.go
• Agent guidance: docs/integrations/SKILLS.md
• Companion packs: vault.*