Transactional email API for AI agents

AgentiSend is a transactional email API for AI agents with a spending limit, a loop guard and a kill switch on every key. Every refusal names the code, the message and the fix.

The five controls

A spending limit is budget_per_period on the key, set with PATCH /limits/keys/{id} and checked before the send; past it the code is agent_budget_exceeded.

A per-minute ceiling is rate_ceiling_per_minute on the same call; past it the code is rate_ceiling_exceeded.

An approval hold answers approval_required. A person sends the held message with POST /agent-actions/{id}/approve or drops it with POST /agent-actions/{id}/reject. GET /agent-actions lists the queue.

The loop guard holds a send that would be the 4th near-identical message to one recipient inside 60 minutes. That hold uses the same approval_required code. The page for a loop that is already running is Stop an AI agent sending emails in a loop.

The kill switch is POST /limits/keys/{id}/kill for one key and POST /limits/kill-all for the account. A paused key is refused with kill_switch_active, and the catalogue fix says only a person signed in to the console can resume it.

curl -sS -X POST https://api.agentisend.com/emails \
  -H "Authorization: Bearer $AGENTISEND_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"from":"billing@yourdomain.com","to":"delivered@simulator.agentisend.com","subject":"Your receipt","text":"Thanks — the details are attached."}'

201
{
  "id": "9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42",
  "simulated": true,
  "warnings": []
}

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

200
{
  "affected_key_ids": [],
  "at": "2026-09-04T09:14:00.000Z",
  "paused": false,
  "reason": "example"
}

The checklist that maps each of those controls to the call is Email API with spending limits for AI agents. The comparison of what to require, across seven options, is Email API for AI agents.

Send from a client

The MCP server is https://api.agentisend.com/mcp and it publishes 92 tools, the same budgets and the same refusals as the HTTP API. Install a client and send one message: Node (agentisend on npm, the same code as @agentisend/sdk-node), Python (pip install agentisend), PHP (composer require agentisend/agentisend-php) or Go. The install lines and the send for each are on SDKs. One page per editor and builder is linked from the hub.

Free plan

Every account starts on the Free plan: 5,000 emails a month, up to 170 a day, on 3 verified domains, at $0. Paid plans start at $9 a month. GET /billing/plan returns the plan on the account.

AgentiSend vs Resend is the row-by-row comparison.

FAQ

What is a transactional email API for AI agents?

AgentiSend is a transactional email API for AI agents. The key carries a spending limit, a loop guard and a kill switch, and a refusal names the fix.

Where is the spending limit set?

On the key, with PATCH /limits/keys/{id}. The limit counts messages, not currency. The longer page is the spending-limits URL linked above.