Lettr API Documentation

This is the complete API documentation for connecting to the Lettr API using MindCloud's Universal API. If you are new to MindCloud, start with the Introduction to see how one API can sit in front of many different apps.

MindCloud is an integration company that offers one normalized API to access 3,100+ apps from a single place. It cleans up provider-specific quirks, keeps requests and responses consistent, and centralizes authentication so you do not need to manage separate flows for every app. Browse other apps.

Meet Lettr: Send transactional and scheduled emails, manage domains, templates, and webhooks with the Lettr REST API. Keep reading to get started.

Quickstart

Before you run your first Lettr request, you need three things:

1. A MindCloud account — sign in or create an account at MindCloud.
2. A MindCloud API Key — create one in API Keys. Keep it on your server.
3. At least one Lettr connection — create or choose one in Connections. Note its connectionId.

Every Lettr action uses the same URL pattern:

https://connect.mindcloud.co/v1/universal/lettr/latest/actions/{actionSlug}

You need a MindCloud API Key and a Lettr connection. Then call an action such as Auth Check:

curl --request GET \
  --url "https://connect.mindcloud.co/v1/universal/lettr/latest/actions/auth-check" \
  --header "Authorization: Bearer $MINDCLOUD_API_KEY" \
  --get \
  --data-urlencode "connectionId=$CONNECTION_ID"

Every response comes back in the same envelope, with your rows in a data array:

{
  "success": true,
  "data": [
    { "id": "1042", "name": "Ava" }
  ],
  "meta": {}
}

After your first request works, use Shape your requests to control arguments, pagination, filtering, fields, and errors.

Authentication

Authentication has two layers. Your MindCloud API Key authenticates the request to MindCloud, sent as a Bearer token in the Authorization header. The connectionId selects the connected Lettr account that should run the action. MindCloud stores and refreshes the Lettr credentials behind that connection, so you never send provider tokens with your requests.

Pass connectionId in the query string for GET and DELETE actions, and in the JSON body for POST, PUT, and PATCH actions. Keep your MindCloud API Key on your server; do not ship it in browser code, mobile apps, public repositories, or logs.

Lettr actions

All 32 published actions for this Lettr version. Each page documents the endpoint, arguments, and response controls.

• GETAuth Check
• DELETECancel Scheduled Email
• POSTCreate Domain
• POSTCreate Template
• POSTCreate Webhook
• DELETEDelete Domain
• DELETEDelete Template
• DELETEDelete Webhook
• GETGet Domain
• GETGet Email Detail
• GETGet Scheduled Email
• GETGet Template
• GETGet Template Merge Tags
• GETGet Template Merge Tags By Version
• GETGet Webhook
• GETHealth Check
• GETList Bounce Events
• GETList Delivery Events
• GETList Domains
• GETList Email Events
• GETList Email Events For Transmission
• GETList Templates
• GETList Webhooks
• POSTSchedule Email
• POSTSchedule HTML Email
• POSTSchedule Template Email
• POSTSend Email
• POSTSend HTML Email
• POSTSend Template Email
• PUTUpdate Template
• PUTUpdate Webhook
• PUTVerify Domain

Related apps

More Communication apps on the Universal API, behind the same REST shape. Or browse all apps.

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