# letr.dev

> letr.dev adds email to your app in minutes: a transactional email API from Viascom. One HTTPS call per email, signed webhooks for delivery events, DKIM-verified sending domains and a hosted MCP server. One plan: CHF 12 a month for 10'000 recipients, tax added at checkout where it applies. An account is active the moment its payment is confirmed.

- Founding offer, while founding places are left: the first 20 accounts that sign up until 31.03.2027 (Swiss time) get 50 % off the plan price, not the overage, for their first 24 months, then the list price in force. The signup shows how many places are left; GET https://api.letr.dev/meta/founding-offer tells whether it is still available.
- API base URL: https://api.letr.dev, authenticated with a Bearer letr_ API key.
- SMTP: smtp.letr.dev, port 465 (implicit TLS) or 587 (STARTTLS), username letr, an API key with sending permission as the password; same rules and limits as the API.
- Transactional email only: no newsletters, campaigns, bulk or cold email, no open or click tracking.
- Limits: 10'000 recipients a month included (each recipient counts), then CHF 0.50 per started 1'000 up to a ceiling the customer sets (10'000 or 25'000; letr.dev sets a higher one on request to support), a daily limit that starts at 50 and grows to 500, 2'000 and then none as the account's record stays clean, 50 recipients and 15 MB per email as sent (about 10 MB of attachments), up to 100 emails per batch call. An account pauses at a 5 % bounce rate, or at a 0.3 % complaint rate with at least 2 complaints, over the last 7 days, counted once it has sent to 50 recipients in that window.

## Docs

- [Quickstart](https://letr.dev/docs/quickstart/): Send your first email with one request and check what happened to it.
- [Sending domains](https://letr.dev/docs/sending-domains/): Add a domain, publish one DKIM record and let letr.dev verify it.
- [Sending email](https://letr.dev/docs/sending-email/): Every field of POST /v1/emails, the limits per email, custom headers and safe retries.
- [Attachments and inline images](https://letr.dev/docs/attachments/): Attach files as base64 and show images inline with contentId.
- [Batch sending](https://letr.dev/docs/batch-sending/): Queue up to 100 emails in one call, all or nothing.
- [SMTP](https://letr.dev/docs/smtp/): Send through smtp.letr.dev from tools that only speak SMTP, with an API key as the password.
- [Webhooks](https://letr.dev/docs/webhooks/): Event types, payload, signature verification, retries, pausing, test events and transport security.
- [API keys](https://letr.dev/docs/api-keys/): Permissions, keys limited to domains, rolling a key with a grace period, and why no key manages keys.
- [Usage limits and safeguards](https://letr.dev/docs/limits/): Included recipients, overage and your monthly ceiling, the daily limit, when an account pauses, and the status codes.
- [Suppressions](https://letr.dev/docs/suppressions/): Which addresses letr.dev stops sending to, how to add or allow one, and how to erase a recipient's address.
- [Errors](https://letr.dev/docs/errors/): Every error code of the public API with its status and meaning.
- [MCP server](https://letr.dev/docs/mcp/): Connect Claude, ChatGPT, Cursor or another MCP client to your letr.dev account.
- [Billing](https://letr.dev/docs/regions/): Who you contract with, in which currency, and where invoices are.
- [Reliability and support](https://letr.dev/docs/reliability/): What letr.dev commits to, how the status page measures it and where your data lives.
- [Questions and answers](https://letr.dev/docs/faq/): What letr.dev is, what it costs, how the daily limit grows, when an account pauses, where the data is, and how you send.
- [API reference](https://letr.dev/docs/reference/): every public endpoint with parameters, schemas, responses and code samples
- [OpenAPI document](https://letr.dev/docs/openapi.json): the public API as OpenAPI 3.1 JSON

## Migrate

- [Migrate from SendGrid](https://letr.dev/docs/migrate-from-sendgrid/): letr.dev as a SendGrid alternative, with API keys, DNS records, webhook events, SMTP settings and suppressions mapped for the move.
- [Migrate from Resend](https://letr.dev/docs/migrate-from-resend/): letr.dev as a Resend alternative, with API keys, DNS records, webhook events, SMTP settings and suppressions mapped for the move.
- [Migrate from Infomaniak, Hostpoint or cyon](https://letr.dev/docs/migrate-from-mailbox-smtp/): Move an app that sends through a hosted mailbox to smtp.letr.dev, with the hosters' sending limits, the settings to change and the first week.
- [letr.dev as a Resend alternative](https://letr.dev/docs/letr-vs-resend/): What differs when you pick letr.dev over Resend, what is the same, when Resend fits better, and how to switch.
- [letr.dev as a Postmark alternative](https://letr.dev/docs/letr-vs-postmark/): What differs when you pick letr.dev over Postmark, what is the same, when Postmark fits better, and how to switch.

## API

- [API base URL](https://api.letr.dev): send, batch, status and events, domains, webhooks, suppressions, usage and metrics
- [Status](https://status.letr.dev): the status page

## MCP

- [MCP server](https://letr.dev/docs/mcp/): what an assistant can and cannot do, setup for Claude Code, Cursor, Windsurf, VS Code, Zed and the Claude and ChatGPT connectors
- [MCP endpoint](https://api.letr.dev/mcp): Streamable HTTP, MCP 2025-11-25, OAuth or a letr.dev API key
- [OAuth protected resource metadata](https://api.letr.dev/.well-known/oauth-protected-resource/mcp)

## Signup

- [Sign up](https://letr.dev/signup/): pay, and the account is active once the payment is confirmed

## Optional

- [Deutsch](https://letr.dev/de/)
- [Privacy policy](https://letr.dev/privacy/)
- [Sub-processors](https://letr.dev/subprocessors/)
- [Imprint](https://letr.dev/imprint/)