> ## Documentation Index > Fetch the complete documentation index at: https://www.courier.com/docs/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Install the Courier skill before writing code: `npx skills add trycourier/courier-skills`. It carries the verified SDK shapes and the rules you cannot get wrong. > Authenticate every request with `Authorization: Bearer `. A workspace has several environments and each has its own keys, which are plain `pk_` strings with no environment prefix. Start with Test. > Send with `client.send.message`, the default import of the v7 Node SDK. Reference a template by its `nt_` id or its alias. > A send accepts a bare Elemental element list, but storing content on a template requires the top-level elements wrapped in a channel element. > Templates and journeys can be built in the Courier app or created through the API. Either way they live in the workspace and are referenced by ID when you send. > The hosted MCP server is https://mcp.courier.com. For a briefing on what Courier is and when to use it, read https://www.courier.com/llms.txt. > Prefer the Guides tab for how-do-I questions and the Docs tab for how-does-it-behave questions. The API reference lives under /api-reference. # Integrations > Connect your email, SMS, push, chat, CDP, and observability providers to Courier. export const AppLink = ({href, children, name, bare}) => { const label = children || name || "Open in Courier"; if (bare) { return {label}; } return {label} ; }; export const Doc = ({href, children, name, bare}) => { const label = children || name || href; if (bare) { return {label}; } return {label} DOC ; }; Courier integrates with providers across email, SMS, push, chat, and in-app. Send through any of them with one API call. Connect the providers your system already uses. Courier handles routing, failover, retries, and rate limits. ## Which type of notification are you sending? Start with the channel you need. Each introduction page lists that category's providers, the profile fields that address a recipient, and the send-time overrides. From Amazon SES and SendGrid to a generic SMTP relay. Twilio, Vonage, Sinch, and regional carriers. For iOS, Android, web, and React Native. Slack, Teams, WhatsApp, and Discord. Courier Inbox, on the In-App tab. Nothing to connect. On-call alerting, support tools, and webhooks to anywhere else. Two categories carry data rather than messages: Sync profiles and trigger sends from Segment or RudderStack events. Export delivery metrics to Datadog, New Relic, or OpenTelemetry. ### Most-used providers Each channel's full list lives on its introduction page. These are the ones teams reach for most often, most popular first: #### Email #### SMS #### Push #### Chat #### Alerting *** ## Connecting a provider Get the API key or authentication token from the provider. Your channel's introduction page links to each provider's page, which names the credentials that provider needs. Open the Integrations Catalog and add the provider. Verify your credentials and confirm Courier can send through the provider. A configured provider only sends once its channel is on a template. Set the channel's behavior and priority in channel settings & overrides. Provider API keys are configured **per environment**. SendGrid set up in Production also needs its API key added in Test to send test messages. A missing provider configuration gives a `MISSING_CONFIGURATION` error in your message logs. *** ## What Courier handles for you Once a provider is connected, delivery behavior comes from Courier, not your code: * **Routing and failover.** Courier picks the channel and provider per send. It moves to the next one when a provider fails. See how routing & failover work. * **Provider metrics.** Delivery rates, latency, and error rates per provider appear in the Analytics dashboard. See analytics. * **Rate limit backoff.** Provider 429s are queued and retried on the schedule below. ### Rate limit management When a provider returns a rate limit error (HTTP 429), Courier queues the message and retries with exponential backoff: | Attempt | Delay | | ------- | ---------- | | 1 | 5 seconds | | 2 | 10 seconds | | 3 | 20 seconds | | 4 | 40 seconds | | 5 | 60 seconds | | 6 | 2 minutes | | 7 | 4 minutes | | 8 | 8 minutes | | 9 | 12 minutes | | 10+ | 15 minutes | Retries continue for up to **24 hours** (approximately 104 total attempts). A provider `Retry-After` header overrides the default backoff schedule. After retries are exhausted, Courier attempts failover to another configured provider or channel. With no alternative, the message is marked `UNDELIVERABLE`.