# StableEmail Subdomain Send

> StableEmail Subdomain Send is a paid API for AI agents from StableEmail at stableemail.dev, paid per call via MPP, $0.005/call, status unknown (last checked 2026-10-09).

Sends an email from a custom subdomain address on stableemail.dev at $0.005 per message

## Facts

- Endpoint: POST https://stableemail.dev/api/subdomain/send?utm_source=zero.xyz
- Price: $0.005/call
- Payment: MPP
- Status: unknown
- Last checked: 2026-10-09
- Activations on Zero: 1
- Provider: StableEmail
- Docs: https://stableemail.dev
- Website: https://stableemail.dev
- Tags: email, send, inbox, forwarding, subdomain, social
- Canonical page: https://www.zero.xyz/c/stableemail-send-d6a260be
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_TG1f7e-5K92tPsAc0RpP-

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability stableemail-send-d6a260be -d '<json body>'
```

Example prompt: Send an email from hello@mycompany.stableemail.dev to alice@example.com with subject 'Your order has shipped' and body 'Hi Alice, your order #1234 is on its way and should arrive by Friday!'

## When to prefer this

Choose this endpoint when you need to send email from a specific custom subdomain address you own on stableemail.dev (e.g. noreply@yourbrand.stableemail.dev), rather than sending via the generic relay@stableemail.dev address. It is cheaper ($0.005 vs $0.02) and provides branded sender identity. Ideal for transactional emails, notifications, and automated outreach where a branded subdomain sender is important and no traditional email API keys or account setup is desired.

## Known failure modes

- Invalid or unauthorized from address (not owned subdomain) — 401/403 error
- Invalid recipient email format — 400 validation error
- Missing required fields (from, to, subject) — 400 error
- Insufficient USDC balance — 402 payment required
- Attachment too large (>5MB per attachment, max 5 attachments) — 400 error
- Too many recipients (>50 in to or cc) — 400 error
- Subject line too long (>998 chars) — 400 error

## How this service works

Send email from your custom subdomain on stableemail.dev ($0.005)

## Output

A confirmation that the email was successfully sent from the specified subdomain address, typically including a message ID or delivery acknowledgment. Costs $0.005 USDC per send.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "required": [
  "from",
  "to",
  "subject"
 ],
 "properties": {
  "cc": {
   "type": "array",
   "items": {
    "type": "string",
    "format": "email",
    "pattern": "^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"
   },
   "maxItems": 50,
   "minItems": 1
  },
  "to": {
   "type": "array",
   "items": {
    "type": "string",
    "format": "email",
    "pattern": "^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"
   },
   "maxItems": 50,
   "minItems": 1
  },
  "from": {
   "type": "string",
   "format": "email",
   "pattern": "^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"
  },
  "html": {
   "type": "string",
   "maxLength": 256000
  },
  "text": {
   "type": "string",
   "maxLength": 256000
  },
  "replyTo": {
   "type": "string",
   "format": "email",
   "pattern": "^(?!\\.)(?!.*\\.\\.)([A-Za-z0-9_'+\\-\\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\\-]*\\.)+[A-Za-z]{2,}$"
  },
  "subject": {
   "type": "string",
   "maxLength": 998,
   "minLength": 1
  },
  "attachments": {
   "type": "array",
   "items": {
    "type": "object",
    "required": [
     "content",
     "contentType",
     "filename"
    ],
    "properties": {
     "content": {
      "type": "string",
      "maxLength": 5000000
     },
     "filename": {
      "type": "string",
      "maxLength": 255,
      "minLength": 1
     },
     "contentType": {
      "type": "string",
      "maxLength": 255,
      "minLength": 1
     }
    }
   },
   "maxItems": 5
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/stableemail-send-d6a260be/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from stableemail.dev](https://www.zero.xyz/host/stableemail.dev/llms.txt)