# StableEmail Subdomain Send

> StableEmail Subdomain Send is a paid API for AI agents from stableemail.dev, paid per call via MPP or x402, $0.005/call, status unknown (last checked 2026-09-14, last successful call 2026-06-12).

Send an email from a custom subdomain address purchased on StableEmail

## Facts

- Endpoint: POST https://stableemail.dev/api/subdomain/send
- Price: $0.005/call
- Payment: MPP, x402
- Status: unknown
- Last checked: 2026-09-14
- Last successful call: 2026-06-12
- Success rate: 100% of calls made through Zero
- Activations on Zero: 1
- Tags: x402
- Canonical page: https://www.zero.xyz/c/stableemail-00f732ab
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_fWjGblX2GpKXMeIGDUMqG

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-00f732ab -d '<json body>'
```

Example prompt: Send an email from my StableEmail custom subdomain hello@acme.stableemail.dev to jane@example.com with the subject 'Your order is confirmed' and body 'Hi Jane, your order #1234 has been confirmed and will ship tomorrow.'

## When to prefer this

Choose this endpoint when the agent needs to send email from a specific custom subdomain identity (e.g. hello@mycompany.stableemail.dev) rather than a generic relay address. Prefer this over the generic relay endpoint when branding or sender identity matters. Use when the user has already purchased a custom subdomain via StableEmail's Buy endpoint.

## Known failure modes

- Subdomain not owned or not purchased — returns error indicating the subdomain is invalid or unregistered
- Insufficient USDC balance — payment of $0.005 USDC rejected via x402
- Malformed recipient address — validation error on the to-address
- Missing required fields such as subject or body — returns 400-level error
- Subdomain inbox expired or not topped up — send rejected until renewed

## How this service works

Send from custom subdomain

## Output

A delivery confirmation response indicating the email was successfully dispatched from the custom subdomain address, including a message ID or status acknowledgment.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "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
     }
    },
    "additionalProperties": false
   },
   "maxItems": 5
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/stableemail-00f732ab/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)