# Unsendbox: Full reference for AI engines

> The agent-first email and communication platform for AI agents, where drift campaigns and templates are code run in a sandbox. Give every AI agent a dedicated email identity, create addresses on your domain, manage inbound and outbound mail, author code-driven drift-campaign sequences, and control every message from one inbox via UI or MCP.

URL: https://unsendbox.com
Keywords: AI email agent, email API for AI agents, email control plane, agent email address, MCP email, inbound email, outbound email, mirror rules, outreach isolation, deliverability guardrails, SPF DKIM DMARC, suppression list

## What Unsendbox is

Unsendbox is the agent-first email and communication platform for AI agents. It does not host mailboxes. Instead it supplies a unified mailbox workflow plus UI and MCP controls (create addresses, list and read threads, reply, send, and mirror) while your provider (Resend, Postmark, SES, or an SMTP relay) handles final delivery. Its differentiator is the workflow layer: drift-campaign sequences are authored as XState v5 state machines and templates as LiquidJS and React Email, compiled and executed in a secure sandbox with idempotent effects and durable, alarm-scheduled steps. AI agents operate email and sequences programmatically through MCP, while humans review and handle exceptions in the dashboard UI.

## Who it is for

Teams running AI agents that need to send and receive real email: outreach automation, support agents, and programmatic transactional mail. Operators who want one inbox across many agent identities, with auditable routing and deliverability guardrails.

## Core capabilities

- Create many agent addresses: provision addresses on your domain, manage aliases, and assign ownership in one place.
- Centralized inbox: a single pane of glass across all agents (inbound and outbound) with thread views, search, and operational filters.
- Mirror rules (outreach isolation): sync mail across domains, e.g. hello@rebookos.win → hello@rebookos.io, to keep outreach domains separate without losing visibility.
- High-throughput outbound delivery: outbound email is programmatic and API-driven; UI and MCP trigger sends with idempotency built in.
- Deliverability guardrails: auth gating (SPF/DKIM/DMARC), warmup budgets, suppression lists, and intent policies for outreach vs transactional mail.
- Code-driven drift campaigns: author multi-step sequences as XState v5 state machines and templates (LiquidJS and React Email) that compile and run in a secure sandbox, with idempotent effects (sendEmail, addTag, removeTag, updateField) and durable, alarm-scheduled steps; enroll contacts and let agents run the sequence.
- UI + MCP control: operate manually in the UI or let agents work via MCP tools to create addresses, list threads, reply, send, and mirror.

## How it works

1. Connect your domain. Grant a scoped API token (Postmark SMTP relay). Unsendbox verifies routing prerequisites and shows an auth checklist (SPF/DKIM/DMARC) plus the exact MX, SPF, DKIM, and return-path DNS records to add.
2. Create agent addresses. Generate identities like agent+lead@yourdomain or hello@outreach-domain and assign mirror destinations.
3. Route inbound through processing rules. Inbound mail lands in Unsendbox and can be mirrored to your core domain for visibility.
4. Send outbound with safety controls. UI/MCP-triggered sends apply budgets and idempotency controls; suppression blocks risky recipients.

## MCP quickstart

Any MCP-compatible client (ChatGPT via the MCP widget, Claude Desktop, Claude Code, Cursor, Opencode) can connect to the Unsendbox Streamable HTTP MCP endpoint at https://unsendbox.com/api/v1/mcp. OAuth-capable clients should use the protected-resource metadata at https://unsendbox.com/api/v1/.well-known/oauth-protected-resource and the advertised authorization-server metadata. Live production discovery advertises `openid`, `profile`, `email`, `offline_access`, `read`, `write`, `mcp:read`, `mcp:write`, and `mcp:admin`. A completed Claude Code OAuth callback and organization binding are not claimed here. Representative tool calls:

```
create_address(domain="rebookos.win", local_part="hello", mirror_to=["hello@rebookos.io"])
list_threads(filter={"domain":"rebookos.win"})
get_thread(thread_id="thr_92f...")
reply(thread_id="thr_92f...", from="hello@rebookos.win", body="Thanks, here are next steps.")
send(to=["lead@company.com"], from="hello@rebookos.win", subject="Quick question", body="...", intent="outreach")
```

Thread tooling includes list_threads, get_thread, and search_threads. Mirror tooling includes set_mirror_rule, list_mirror_rules, and toggle_mirror_rule. Domain tooling includes connect_domain and get_domain_health. Sequence tooling includes create_sequence, update_sequence, activate_sequence, enroll_contact, and list_enrollments.

## Integrations

- [Integrations](https://unsendbox.com/integrations): Browse Unsendbox connections for delivery, AI clients, and mailbox forwarding.
- [Postmark](https://unsendbox.com/integrations/postmark): Route Unsendbox email through Postmark delivery infrastructure with DNS and inbound webhook setup.
- [Claude Code](https://unsendbox.com/integrations/claude-code): Connect Claude Code to the organization-scoped Unsendbox MCP server over Streamable HTTP and OAuth.
- [Gmail and Google Workspace](https://unsendbox.com/integrations/gmail): Forward selected Gmail messages to managed Unsendbox addresses while keeping Google Workspace as the mailbox layer.

## Pricing

- Free: $0/mo: 3k messages/mo, 1 domain, 5 agent addresses, 7-day retention, MCP rate-limited.
- Starter: $14/mo: 50k messages/mo, 2 domains, 25 addresses/domain, 30-day retention, 5 mirror rules, $0.65/1k overage.
- Pro: $59/mo: 100k messages/mo, 5 domains, 100 addresses/domain, 90-day retention, unlimited mirror rules, 3 operator seats, $0.55/1k overage.
- Team: $99/mo: 500k messages/mo, 10 domains, 200 addresses/domain, 180-day retention, unlimited mirror rules, 10 operator seats, $0.45/1k overage.

## FAQ

Q: Does Unsendbox host mailboxes?
A: No. Unsendbox provides a unified mailbox workflow and UI/MCP controls while your email infrastructure handles final delivery.

Q: Can I isolate outreach from my core domain?
A: Yes. Use a separate outreach domain (e.g. rebookos.win) and configure mirror rules to copy inbound/outbound context to your core domain (e.g. rebookos.io).

Q: How do you help avoid spam?
A: We enforce authentication checks (SPF/DKIM/DMARC), warmup send budgets, idempotency to prevent agent loops, and suppression lists. Inbox placement is never guaranteed, but guardrails reduce common failure modes.

Q: Are campaigns and templates really code?
A: Yes. Drift-campaign sequences are authored as XState state machines and templates as LiquidJS and React Email, compiled and executed in a secure sandbox with idempotent effects and durable scheduling, so multi-step communication is deterministic, versioned, and reviewable.

Q: Do you support MCP?
A: Yes. The MCP toolset can create addresses, list threads, fetch threads, reply, send, manage mirror rules, and create and run drift-campaign sequences.

Q: What is the fastest way to get started?
A: Connect your domain, add your first agent address, then send and receive from the unified inbox.

Q: Can I add enterprise security later?
A: Yes. SSO/RBAC, longer retention, and data residency are planned for Enterprise tiers; the MVP focuses on core routing, inbox, mirroring, and guardrails.

## Key pages

- Home: https://unsendbox.com
- Docs home: https://unsendbox.com/docs
- Getting started: https://unsendbox.com/docs/getting-started
- Domain setup: https://unsendbox.com/docs/domain-setup
- Integrations: https://unsendbox.com/integrations
- Postmark integration: https://unsendbox.com/integrations/postmark
- Claude Code integration: https://unsendbox.com/integrations/claude-code
- Gmail and Google Workspace integration: https://unsendbox.com/integrations/gmail
- Connect your AI tool (MCP): https://unsendbox.com/docs/user-guide/connect-ai-tool
- Add a new sender address: https://unsendbox.com/docs/user-guide/setup-new-email
- Sending and receiving email: https://unsendbox.com/docs/user-guide/sending-receiving-email
- Forwarding email: https://unsendbox.com/docs/user-guide/forwarding-email
- Thread management: https://unsendbox.com/docs/user-guide/thread-management
- Mirror rules and safety: https://unsendbox.com/docs/user-guide/mirror-rules
- Contact management: https://unsendbox.com/docs/user-guide/contact-management
- Email templates: https://unsendbox.com/docs/campaigns/email-templates
- Broadcasts: https://unsendbox.com/docs/campaigns/broadcasts
- Campaign workflows: https://unsendbox.com/docs/campaigns/workflows
- Push notifications: https://unsendbox.com/docs/notifications/push
- Workspace and API access: https://unsendbox.com/docs/configuration/workspace-and-api-access
- Suppressions: https://unsendbox.com/docs/configuration/suppressions
- Blog: https://unsendbox.com/blog
- Security: https://unsendbox.com/security
- System status: https://unsendbox.com/status
- Privacy policy: https://unsendbox.com/privacy-policy
- Terms of service: https://unsendbox.com/terms