POST /domains

Request

The same call in curl, Node and Python. A path id in the sample is a placeholder.

curl

curl -sS -X POST https://api.agentisend.com/domains \
  -H "Authorization: Bearer $AGENTISEND_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"name":"example"}'

Node

import { AgentiSend } from 'agentisend';

const client = new AgentiSend(process.env.AGENTISEND_API_KEY);
const result = await client.request({
  method: 'POST',
  path: '/domains',
  body: {
    "name": "example"
  },
});

Python

import json, os, urllib.request

url = 'https://api.agentisend.com/domains'
headers = {'Authorization': 'Bearer ' + os.environ['AGENTISEND_API_KEY']}
payload = json.dumps({"name":"example"}).encode()
headers['Content-Type'] = 'application/json'
request = urllib.request.Request(url, data=payload, headers=headers, method='POST')
print(urllib.request.urlopen(request).read().decode())

Tag: domains. Generated from openapi.json; the anchor post-domains is the id the console's error fix links point at.

Parameters

• Idempotency-Key header · string · optional — Makes this call safe to retry. Send the same key with the same body and the original response is replayed instead of the work happening twice. Keys are 1-256 characters and are remembered for 7 days. While the first attempt is still running, a second call with that key returns 409 idempotency_in_flight (Resend calls this concurrent_idempotent_requests); the same key with a different body returns 409 idempotency_payload_mismatch (Resend: invalid_idempotent_request). Resend-Idempotency-Key is accepted as the same header.
• Resend-Idempotency-Key header · string · optional — Alias of Idempotency-Key. Idempotency-Key wins if both are sent.

Request body

Responses

• 201 — Success
• 400 — The request is malformed or a field failed validation. Codes: validation_error, invalid_idempotency_key, invalid_cursor, plan_not_purchasable, stripe_signature_invalid, support_upload_rejected, appsumo_license_not_confirmed, appsumo_ticket_invalid, sign_in_check_required.
• 401 — No usable credential was sent. Codes: agent_signup_code_rejected, missing_api_key, session_required, mfa_required, appsumo_signature_invalid.
• 403 — The credential may not do this, or the account or key is stopped. Codes: sending_domain_blocked, young_domain_held, domain_sending_disabled, inbound_sender_refused, domain_not_verified, onboarding_recipient_not_a_member, onboarding_sender_unavailable, account_suspended, account_sandboxed, agent_unconfirmed, recipient_ramp, human_action_required, csrf_origin_rejected, charge_not_this_account, invalid_api_key, restricted_api_key, insufficient_role, invite_email_mismatch, domain_scope_violation, dedicated_ip_assigned_by_us, approval_required, staff_review_required, trust_paused, kill_switch_active.
• 404 — Nothing with this id exists on the account. Codes: billing_customer_missing, not_found, session_expired, support_ticket_not_found.
• 409 — The request conflicts with the current state. Codes: domain_already_exists, template_name_taken, template_alias_taken, template_in_use, segment_in_use, contact_resubscribe_required, email_still_scheduled, domain_verified_elsewhere, domain_not_claimable, return_path_subdomain_in_use, overage_not_on_plan, term_not_on_sale, subscription_active, portal_change_unavailable, already_in_account, idempotency_in_flight, idempotency_payload_mismatch, approval_expired, support_closed, support_reopen_expired, support_merge_conflict, support_reply_too_soon, appsumo_license_linked, appsumo_license_inactive, lifetime_sold_on_appsumo.
• 413 — The request body is larger than this operation accepts. Codes: payload_too_large, support_upload_too_large.
• 415 — The request body is not JSON. Codes: unsupported_media_type.
• 422 — A field is well formed but was refused. Codes: missing_required_field, invalid_from_address, invalid_parameter, invalid_attachment, invalid_region, tracking_subdomain_unverified, tracking_subdomain_cannot_be_removed, domain_field_immutable, open_tracking_on_transactional, header_replaced, html_clipped_by_gmail, link_domain_listed, domain_blocklisted, mailbox_provider_domain, onboarding_shape_refused, dkim_key_mismatch, domain_check_window_expired, spf_conflict, spf_lookup_limit, review_sandbox_recipient_only, suppressed_recipient, agent_signup_refused, content_refused, recipient_blocklisted, last_owner_required, seat_limit_reached, invite_not_valid, key_budget_exceeds_plan, domain_limit_reached, webhook_endpoint_limit_reached.
• 429 — A rate, quota or ramp ceiling was reached. Codes: onboarding_daily_cap_reached, trust_throttled, invite_limit_reached, rate_ceiling_exceeded, daily_quota_exceeded, monthly_quota_exceeded, rate_limit_exceeded, support_rate_limited, appsumo_lookup_limited.
• 500 — Something failed on our side. Codes: internal_server_error.

Response headers

• ratelimit-limit — Messages this API key may spend in one 60-second window.
• ratelimit-remaining — Messages left in the current window.
• ratelimit-reset — Seconds until the current window resets and the budget refills.

Response example

201
{
  "capabilities": {
    "receiving": "enabled",
    "sending": "enabled"
  },
  "click_tracking": false,
  "created_at": "2026-09-04T09:14:00.000Z",
  "dkim_selector": "example",
  "id": "9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42",
  "inbound_hold_mode": "monitor",
  "inbound_policy": "open",
  "inbound_refused_count": -9007199254740991,
  "name": "example",
  "object": "domain",
  "open_tracking": false,
  "provider_hints": {
    "cloudflare": "example",
    "godaddy": "example",
    "namecheap": "example",
    "route53": "example"
  },
  "recent_events": [],
  "records": [],
  "region": "us",
  "return_path_subdomain": "example",
  "status": "pending",
  "tls_mode": "opportunistic",
  "tracking_issues": [],
  "tracking_subdomain": "example",
  "verified_at": "2026-09-04T09:14:00.000Z",
  "warnings": [],
  "zone": "example"
}

Errors

The codes this operation can answer with, and what to do about each. Every one arrives with its code, message, fix and docs_url.

• csrf_origin_rejected (403) — This request came from a page on another site, and it changes data. Fix: Call the API with an API key (Authorization: Bearer …) instead of a session cookie, or make the request from the console. Create a key in the console under Settings, API keys.
• domain_already_exists (409) — That domain is already registered on this account. Fix: Use the existing domain from GET /domains. A person removes a domain in the console under Domains.
• domain_blocklisted (422) — This domain is on a public blocklist, so it cannot be added. Fix: Use a domain that is not listed, or wait until the listing is removed, then POST /domains again.
• domain_limit_reached (422) — This plan has no sending domain left. Fix: Remove a domain in the console under Domains, or upgrade in Settings → Billing.
• idempotency_in_flight (409) — A request with this Idempotency-Key is still in progress. Fix: Wait and retry with the same Idempotency-Key to receive the original response.
• idempotency_payload_mismatch (409) — Same Idempotency-Key was used with a different payload. Fix: Reuse the exact same body for retries, or send a new Idempotency-Key for a new request.
• insufficient_role (403) — Your role on this account cannot make this change. Fix: Ask an owner to make the change, or to raise your role with PATCH /team/members/:id.
• internal_server_error (500, internal_server_error) — Unexpected error. Fix: Retry ONCE after a short pause, with the same Idempotency-Key so the retry cannot double-send. If it fails again, stop retrying and report the x-request-id from the response — that id is what identifies this exact failure in support.
• invalid_api_key (403, invalid_api_key) — API key is invalid or revoked. Fix: Create a new key with POST /api-keys; deleted keys cannot be restored.
• invalid_idempotency_key (400) — Idempotency-Key must be 1-256 characters. Fix: Send a non-empty Idempotency-Key header of at most 256 characters.
• invalid_parameter (422) — A parameter has an invalid value. Fix: Correct the named parameter and retry.
• invalid_region (422) — Region must be one of us, eu. Fix: Pass region as us or eu in POST /domains. Omitting it stores us. For this release us-east-1, sa-east-1 and ap-northeast-1 map to us, and eu-west-1 maps to eu.
• mailbox_provider_domain (422) — You cannot send as a mailbox provider’s domain. Fix: Add a domain you own with POST /domains, such as acme.com or mail.acme.com, and send from an address on it.
• mfa_required (401) — This session has not completed two-factor authentication. Fix: Finish signing in at https://console.agentisend.com/verify with a code from your authenticator app, or one of your recovery codes. Manage the second factor in the console under Settings, Security.
• missing_api_key (401, missing_api_key) — Missing API key in authorization header. Fix: Create an API key at https://console.agentisend.com/api-keys and send "Authorization: Bearer as_...". MCP clients can connect with OAuth instead of a key.
• not_found (404, not_found) — Endpoint or resource does not exist. Fix: List that resource on this account and use an id from the list. For a domain, GET /domains accepts the id or the domain name. A path that is not a route is a typo in the URL.
• payload_too_large (413) — Request body is larger than this endpoint accepts. Fix: Send a smaller body. Most endpoints accept 1 MB. Sends (POST /emails, /emails/batch, replies) and template, broadcast and automation edits accept 50 MB, which fits 40 MB of attachments after base64. /mcp accepts 1 MB per JSON-RPC call.
• rate_limit_exceeded (429, rate_ceiling_exceeded, rate_limit_exceeded) — Too many requests. Fix: Back off and retry honoring the Retry-After header.
• restricted_api_key (403, restricted_api_key) — This API key is restricted to sending only. Fix: Use a full_access key (POST /api-keys with permission=full_access) for management endpoints.
• return_path_subdomain_in_use (409) — The return-path host already has an MX record pointing somewhere else. Fix: Pass return_path_subdomain on POST /domains: a label of up to 63 characters that starts with a letter. send is the default; bounce is the usual choice when send already has an MX.
• sending_domain_blocked (403) — This domain cannot send through AgentiSend. Fix: Send from a different domain you own. If you believe this is a mistake, contact support and name the domain.
• unsupported_media_type (415) — This endpoint does not accept that content type. Fix: Send the body as JSON with `Content-Type: application/json`.
• validation_error (400, domain_not_verified, invalid_parameter, validation_error) — Error in one or more fields. Fix: Correct the fields listed in the error details and retry the request.