Ada Lovelace
To: Acme Billing
Hello,
The VAT line on invoice 4192 looks doubled, so the total is higher than the quote. Could you check it before Friday?
Thanks, Ada
The mailbox, as an API
Every inbox is an endpoint.
A REST API, a typed SDK, a command line, webhooks and an MCP server over the same mailbox the app uses. Code, agents and people all drive one inbox.
npm install @nextmail/sdkRuns where you deploy, and inside the tools you build with.
- Node.js
- Bun
- Deno
- Cloudflare Workers
- TypeScript
- Python
- Ruby
- PHP
- Go
- Java
- C#
- Claude Code
- Cursor
- Codex
- GitHub Copilot
- Windsurf
- Gemini CLI
- v0
- Bolt
- Lovable
- Base44
- Modulify
- Replit
- MCP
Four doors.
One mailbox behind them.
REST, the SDK, the command line and MCP reach the same operations, with the same scopes and the same limits.
Your mailbox
msg_4b7e05d3862c1f0a44b19e2csent
Same mailbox, whichever door the message came through.
Write one call.
Delivery is on us.
Anything that speaks HTTP can send. TypeScript, Python, Ruby, PHP, Go, Java and C# get typed clients, and every message reports back as it is queued, sent and delivered.
What happens next
- Request acceptedmsg_4b7e…
- Queuedemail.queued
- Sentemail.sent
- Deliveredemail.delivered
Everything the app does,
your code does.
Threads, search, labels, drafts and contacts are calls too, on the mailbox your team already reads.
What your clicks call
Numbers you can
check from a terminal.
The OpenAPI 3.1 document is public and needs no key, and the SDK has to match it before a release.
- documented operations
- 548
- GET /openapi.json
- paths on one host
- 404
- jq '.paths | length'
- SDK methods
- 684
- Matched to the spec before every release
- MCP tools
- 501
- nextmail mcp tools
- webhook events
- 51
- Matched to the spec before every release
Send once.
Exactly when you meant to.
A retry never sends twice, a send can wait up to a year, and an undo window lasts up to fifteen minutes.
invoice.ts
await nextmail.emails.send({ from: 'Acme Billing <billing@acme.com>', to: 'ada@example.de', subject: 'Your September invoice', html: invoiceHtml,1
attachments: [{ fileId: invoicePdf.id }],}, {2
idempotencyKey: 'invoice:inv_2026_09_4192',})What happens
- 09:41:02status: sent
Accepted and sent. The PDF is large, so it travels as a download link.
- 09:41:07timeout
The connection drops before your code reads the answer.
- 09:41:08Idempotency-Key
The SDK sends it again with the same key.
- 09:41:08replayed: true
Nextmail returns the first result instead of sending twice.
A retry never sends twice.
Every delivery signed.
Every retry, the same id.
51 events, signed with HMAC, retried up to eight times over about 27 hours, and replayable.
Deliveries
Every POST to acme.com, newest first.
Every door,
up close.
Use the typed SDK, script the CLI, connect an agent over MCP, or speak plain HTTP.
TypeScript SDK
A client with zero dependencies for Node 20 and up, Bun, Deno and Cloudflare Workers.
Read the docs: TypeScript SDKCommand line
Every SDK method is a command, with --json, --dry-run and exit codes.
Read the docs: Command line501 tools
MCP server
Point a client at one URL and sign in. The tools follow what you approve.
Read the docs: MCP serverAPI keys
Scoped keys with a sending address, an expiry and a log of every request.
Read the docs: API keysOpenAPI 3.1
The whole contract is one public document, readable without a key.
Read the docs: OpenAPI 3.1Paste one prompt
into the tool you build with.
Coding agents and app builders wire up sending from a single prompt. Your key stays on the server.
Switching
Coming from another provider?
Keep your code.
Pick the one you are leaving. Your code converts call by call, contacts, templates and webhooks come across with one key where the provider allows it, and old mail is copied from the old mailbox or an export.
