SadaSend is the transactional email API with built-in safety guardrails, built for developers and engineering teams who want to prevent accidental staging leaks and runaway AI loops.
Give your agent email.
Keep your peace of mind.
The transactional email API with built-in safety guardrails. Per-key recipient allowlists, 1-click Slack approvals, and a hosted MCP server—so AI agents and staging runs never accidentally email real customers.
6,000 emails free · no card · every guardrail on every plan
// The safety rules, set once when the key is created.
// The agent gets the key. It cannot widen any of this.
{
scopes: ['send', 'read', 'domains'], // all 12 safe tools
allowlist: ['@yourteam.com'], // who it may reach
rateLimitMax: 50, // how fast
rateLimitWindow: '1h',
mode: 'approval', // who signs off
}Deliverability protected by architecture and automatic pre-send checks
Major mailbox providers (Gmail, Yahoo, Apple, Microsoft) immediately drop non-compliant traffic. SadaSend verifies SPF/DKIM/DMARC alignment, injects one-click unsubscribes, and monitors complaint rates automatically before any email is delivered.
- SPF · DKIM · DMARC
- Cryptographically verified before your first production email is sent
- RFC 8058 Unsubscribe
- Machine-readable one-click unsubscribe headers injected automatically
- Complaint Guard
- Monitored across a rolling 7-day window (evaluated every 5 min): warning at 0.08%, throttling at 0.10%, suspension at 0.25%
- Instant Suppression
- Hard bounces and complaints automatically suppressed account-wide
Traditional email APIs grant all-or-nothing access. SadaSend gives you built-in safety controls.
Handing an AI agent an ordinary API key lets it email anyone in the world if it loops or hallucinates. SadaSend provides built-in safety controls—recipient allowlists, hourly send caps, and 1-click approval holds—included on every plan.
keys.createEnforced at the API before the send reaches the queue — not in a doc, not in a lint rule, and not dependent on the agent behaving.
Every safety gate can be configured per API key via the developer dashboard or REST API.
Read security & safety gate documentationSimulate Runaway Agents & Staging Leaks
Explore simulated server-enforced safety guardrails right in your browser. Watch how velocity tripwires and allowlists cut off hallucinated dispatches before an email can leak.
Simulate Agent Infinite Hallucination Loop
An LLM agent gets stuck in a recursive loop and attempts to send dozens of emails in rapid succession.
0 / 5 max
0
Click "Trigger Loop" to simulate a runaway agent send burst.
Observes exact status codes and error responses.
The surfaces where you approve, inspect, and debug
Automated email should never be a black box. Inspect the real dashboard interfaces where your team clears autonomous agent drafts, audits DKIM alignment, and reviews edge delivery telemetry.
Every held message can be cleared through the web UI or automatically via authenticated webhook triggers.
Explore architecture documentationHow SadaSend prevents runaway email
The barrier sits in front of the queue, not in a prompt or system instructions. Every send is checked by server rules before anything is dispatched.
Agent initiates tool call
Your agent (Claude, Cursor, LangChain) invokes send_email with recipient and body. It cannot alter the key’s preset limits.
SadaSend evaluates policy gate
Every send is verified against the key’s server-enforced scopes, recipient allowlist, hourly rate limits, and suppression history.
Instant dispatch or human sign-off
Allowlisted transactional sends are accepted and queued immediately. Out-of-allowlist sends are blocked; keys configured in approval mode hold dispatches in pending_approval for 1-click human clearance.
- Zero LLM Training
- Customer email content, variables, and payloads are never used to train or fine-tune models.
- Server-Enforced Key Scopes
- Agents hold keys that can only send or read — never mint keys, delete domains, or remove suppressions.
- Cryptographic Webhooks
- HMAC-SHA256 signatures with timestamp replay protection on all delivery events.
- Append-Only Audit Log
- Every attempt, blocked send, and delivery event is recorded with millisecond precision for audit inspection.
Want to see how our edge proxy enforces rate limits, token scopes, and allowlists?
Read full architecture specificationsUnder ten lines to a delivered email
Install, set a key, send. Zero-dependency official TypeScript and Python SDKs live on npm and PyPI, alongside our hosted Model Context Protocol (MCP) server for AI agents.
https://mcp.sadasend.com// Universal Model Context Protocol (MCP) Server for AI Agents
// Native integration for Antigravity, Cursor, Cline, Windsurf & Claude
{
"mcpServers": {
"sadasend": {
"url": "https://mcp.sadasend.com",
"headers": {
"Authorization": "Bearer $SADASEND_API_KEY"
}
}
}
}
// 12 email tools: send_email, preview_email, verify_email, get_stats, etc.Looking for full API schemas, error codes, webhook verifiers, or MCP tools?
Explore all documentationSeamless integration with the tools modern teams run on
Whether you dispatch from high-growth CRMs, visual automation pipelines, autonomous AI agent frameworks, or developer IDEs, SadaSend connects in seconds via REST API, Port 587 ESMTP, or native Model Context Protocol (MCP).
The leading modern open-source CRM (React/GraphQL). Route transactional updates, deal notifications, and customer emails with zero SMTP rate-limiting.
- Custom SMTP relay
- Zero Gmail rate limits
- Verified custom DKIM
The next-gen relational CRM for tech startups. Dispatch transactional customer sequences, onboarding alerts, and billing receipts via low-latency REST.
- 202 Accepted async queue
- Webhook event feedback
- Domain reputation isolation
Connect SadaSend as your dedicated transactional delivery engine for HubSpot workflows, password resets, and receipts with zero marketing stream bleed.
- Dedicated transactional stream
- STARTTLS encryption
- 100% SPF/DKIM alignment
Enterprise Service Cloud and CRM notification gateway. Enforce server-enforced recipient allowlists and tamper-proof delivery audit trails.
- Per-key recipient allowlists
- FCrDNS authenticated IPs
- Full delivery telemetry
Modern contact and relationship CRM. Send transactional messages and team notifications without risking your primary Google Workspace domain.
- Subdomain isolation
- Instant API key minting
- 6,000 free monthly sends
Automate transactional notifications, invoice dispatches, and alert workflows in n8n with zero SMTP socket timeouts or Gmail rate traps.
- Native HTTP request node
- Auto retry with DLQ
- Zero socket timeouts
Plug SadaSend into visual scenarios using the HTTP request module. High throughput, zero account freeze risks, and real-time webhook sync.
- JSON body templates
- Instant delivery tracking
- High burst capacity
Trigger transactional receipts, alerts, and invitations from 8,000+ apps. Deliver reliably with 202 Accepted durability and automated suppressions.
- Catch Hook triggers
- Structured metadata
- Bilateral webhook sync
Integrate in under 60 seconds across your stack
Standard SMTP Relay (Twenty CRM, HubSpot, Supabase)
host: smtp.sadasend.com
port: 587
security: STARTTLS
user: apikey
pass: $SADASEND_API_KEY # Scoped to recipient allowlistA hosted MCP server with built-in safety controls
Connect Claude, Cursor, Windsurf, or custom AI agents in one command. Your agent gets twelve safe tools to compose, preview, verify, and monitor email — with zero access to credential generation, domain deletion, or suppression tampering.
claude mcp add --transport http sadasend https://mcp.sadasend.com| Tool | Scope | Does |
|---|---|---|
| send_email | send | Send one, honouring key mode and allowlist |
| preview_email | send | Dry run — render and validate, never send |
| get_email_status | read | Delivery state and full event trail |
| search_emails | read | Filtered log search — the debugging workhorse |
| list_domains | read | Which domains are verified — the first check when a send is refused |
| check_domain_setup | domains | Per-record DNS diagnosis, with the fix |
| list_templates | read | Templates on the account, with the variables each expects |
| check_suppression | read | Is this address suppressed, and why |
| render_template | read | Preview a template without sending |
| get_stats | read | Bounce and complaint rates for a window |
| build_utm_url | read | Build and normalize standardized UTM campaign URLs with validation |
| verify_email | read | Pre-flight MX DNS lookup, RFC syntax check, and disposable detection |
There is no create_api_key, no delete_domain, and no remove_suppression tool. An agent that can mint its own credentials or un-suppress a complainer has no safety limits. Those operations live exclusively in the dashboard under authenticated human control.
- “Send the welcome email to the three users who signed up this morning.”
- “Why did our password reset to dana@example.com bounce yesterday?”
- “Check whether our DNS is set up correctly for sending.”
- “Show me every email that bounced this week, grouped by reason.”
Ready to connect Antigravity, Cursor, Windsurf, or Claude Desktop?
Deliverability tools that tell you the fix
The same verification engine that onboards sending domains. Free, no sign-up, no email capture — up to 5 checks/day anonymously (or 100/mo free with an account).
- SPF checkerResolves every include and counts your lookups against the limit of ten.
- DKIM validatorFetches the selector, checks the key length, verifies a signature.
- DMARC checkerParses your policy and tells you what it actually does to failing mail.
- MX lookupResolves the chain and flags misconfigurations.
- Blocklist checkQueries the major blocklists for an IP or domain.
- Inbox placement testInteractive placement simulation across major mailbox providers.
- Email deliverability checkerReal-time syntax validation, MX lookup, typo autocorrect, and burner shield.
- Disposable email checkerNewDetects temporary, throwaway burner addresses before they bounce.
- All diagnostic toolsComplete directory of free deliverability utilities, syntax validators, and DNS checkers.
Where we excel, and where others focus
Every row in our column is a capability you can check against the live API today, not a roadmap. If you need a drag-and-drop newsletter builder for marketing campaigns, tools like SendGrid or Loops are built for that. But if you want to replace both legacy email APIs and costly list cleaners like NeverBounce with native pre-send shields, a built-in Verification Studio, server-enforced AI agent allowlists, and a hosted MCP server, choose SadaSend.
| Capability | SadaSend | Resend | SendGrid | Postmark | Mailgun | Loops |
|---|---|---|---|---|---|---|
| Transactional email API | Yes | Yes | Yes | Yes | Yes | Yes |
| Hosted MCP server | Yes | Yes | No | Partial | Partial | Yes |
| Per-key recipient allowlist | Yes | No | No | No | No | No |
| Agent approval mode | Yes | No | No | No | No | No |
| Dry run / simulation send | Yes | Partial | No | No | No | No |
| Scoped API keys | Yes | Yes | Yes | Partial | Partial | No |
| Per-key velocity & rate limit | Yes | No | No | No | No | No |
| Pre-send bounce shield | Yes | No | Partial | No | Partial | No |
| Built-in list verification studio | Yes | No | Partial | No | Partial | No |
| ESMTP relay (port 587 TLS) | Yes | Yes | Yes | Yes | Yes | Partial |
| Free deliverability tools | Yes | No | No | Partial | No | No |
| Marketing campaign suite | No | Yes | Yes | No | Partial | Yes |
| Visual email designer | No | Yes | Yes | No | Yes | Yes |
Real engineering signals, zero synthetic testimonials
We removed fabricated logos and paid endorsements. Instead, inspect live edge latency measured directly from your browser, install our open SDKs from standard registries, and audit transparent deployment history.
Round-trip latency measured directly from your browser to the European Hetzner edge gateway.
Rolling 90-day gateway availability. Automated health checks monitor ESMTP 587, REST API, and Hosted MCP every 60s.
Every release verified with 380+ unit and Playwright end-to-end integration tests prior to atomic blue/green switchover.
Enterprise-grade safety on an indie budget
Every guardrail and all twelve MCP tools are included on every tier, including the free plan. We do not gate safety behind expensive enterprise sales calls or force multi-tenant users onto degraded, unmonitored pools.
- Full Model Context Protocol (MCP) server (Claude, Cursor & AI runtimes)
- Every agent guardrail: Scoped keys, recipient allowlists, approval mode & dry run
- 6,000 monthly dispatches with 200 emails/day burst ramp protection
- 100 pre-send email verifications / mo (real-time syntax, MX & burner checks)
- 3 verified sending domains with automatic SPF, DKIM & DMARC diagnosis
- Official zero-dependency SDKs (TypeScript & Python) + REST API & SMTP
- 30-day message & log retention
- Single-seat developer workspace (expandable with paid plans)
- Everything in Free, with complete agent safety guardrails
- Slack 1-Click Interactive Approvals (review & release held agent emails in Slack)
- 15,000 monthly dispatches (burst-exempt with no daily volume caps)
- 1,000 pre-send email verifications / mo + Batch CSV list cleaner (100 / batch)
- 6 verified sending domains with automated DNS diagnostics
- 3 signed webhook endpoints with signature verification & event replay
- 25 versioned Liquid templates with typed template variables
- 30-day message & log retention
- Transparent pay-as-you-go elastic top-ups ($0.60 per 1,000 or credit packs)
- Free white-glove migration assistance from legacy providers
- Everything in Starter, with priority routing
- 75,000 monthly dispatches with high-throughput dispatch concurrency
- 10,000 pre-send email verifications / mo + Batch CSV list cleaner (1,000 / batch)
- 25 verified sending domains
- 60-day message & log retention
- 10 signed webhook endpoints with windowed dead-letter replay
- 100 versioned Liquid templates
- Discounted elastic overage ($0.50 per 1,000) & prepaid credit packs
- Priority developer support via dashboard ticket & engineer response
- Everything in Pro, with dedicated infrastructure routing
- 250,000 monthly dispatches on our highest priority sending queue
- 50,000 pre-send email verifications / mo + High-speed batch cleaner (10,000 / batch)
- Unlimited verified sending domains
- 90-day message & log retention
- 25 signed webhook endpoints with automated anomaly throttling
- Unlimited versioned templates
- Best value overage ($0.40 per 1,000) & high-volume credit packs
- Priority developer support & fast engineer escalation
Start on the free plan without a credit card. Yearly billing saves 15% on Starter and Pro, 20% on Scale. Transparent overage: $0.60, $0.50, or $0.40 per thousand emails by plan, billed only for what you send. Zero per-seat charges, ever.
Straight answers
Each answer stands on its own, so you can quote it without the rest of the page.
https://mcp.sadasend.com and your agent instantly receives twelve safe tools: send, preview dry run, email search, delivery status check, template rendering, domain verification, and DNS diagnostics. Destructive operations like creating API keys, deleting domains, or clearing suppressions are architecturally absent from the MCP server, ensuring your agent cannot exceed its mandate.*@yourcompany.com). Any send attempt outside the allowlist is refused synchronously at the API boundary before entering the delivery queue. For sensitive workflows, enable human approval mode to hold emails in a pending_approval state until verified via your dashboard or webhook.smtp.sadasend.com on port 587 with STARTTLS, using your API key as the password. Every guardrail—scopes, allowlists, suppressions, and rate limits—is enforced on SMTP identically to our REST API. Migrate in seconds without changing your application code.npm install sadasend / bun add sadasend) and Python (pip install sadasend) SDKs are live on npm and PyPI with zero third-party runtime dependencies. They include typed exceptions, automatic idempotency keys, and server-enforced agent guardrails. You can also integrate via standard REST API (fetch/cURL), SMTP on port 587, or our hosted Model Context Protocol (MCP) server for AI agents.Stop worrying about runaway email. Ship today.
Generate a scoped API key, set your recipient allowlist, and point your agent or backend at SadaSend. 6,000 emails free forever with zero credit card required.
- 6,000 emails free forever
- All 12 MCP tools included
- Every guardrail active on Day 1
- No credit card required