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Use a connection endpoint to check a credential before running a workflow. The response identifies the team and credential, lists its permissions, and provides a connection label.

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Choose the endpoint

Use the same credential for the connection test and the workflow. A send-only key does not need a Management key to connect. Root API keys are rejected by the Mailbox connection endpoint; mailbox keys are rejected by the Management connection endpoint. These checks do not send email, check credits or provider readiness, read mailbox storage, or require a mailbox selection. A successful connection test confirms authentication for that API. Each workflow action still enforces its permissions and service requirements.
GET /mailbox/me remains available for mailbox details and storage usage. Use GET /mailbox/connection when testing authentication.
For user-approved access, complete OAuth authorisation and use the resulting access token in the same connection test.

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Configure the connection test

1

Store the credential

Create a key with the permissions your workflow needs under API Keys in the Sendmux app. Save it in your integration platform’s credential store.
2

Make an authenticated GET request

Select the endpoint above and send Authorization: Bearer followed by the credential. The request needs no body or query parameters.
3

Read the result

Accept an HTTP 200 response with ok: true. Use data.label as the display label, data.team.id as the stable account identifier, and data.credential.id when you need to distinguish credentials for the same team.
For example, with a Sending key stored in the SENDMUX_API_KEY environment variable:

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Response fields

The response uses the standard { ok, data, meta } envelope. The response does not expose the key creator’s profile, a credential secret, or a mailbox password. A credential identifies access to a team or mailbox; it does not necessarily identify a human user.

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Handle connection failures

Do not shorten the server’s retry interval or disconnect a saved credential because of a temporary 429 or 503 response. If your workflow cannot wait that long, report the delay and retry later. Authenticated responses include Cache-Control: no-store. Authentication is checked again on conditional requests using If-None-Match; a matching representation returns a bodyless 304. Omit this header for a connector’s initial connection test so it receives the response fields.

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Automation platforms

For viaSocket, Zapier, Make, n8n, or Activepieces, configure the platform’s API-key connection test with the same GET request and response-field mapping above. This is also suitable for a custom HTTP workflow. Keep connection validation separate from sending a test email. Use credentials scoped to the actions your integration exposes. Platform-specific OAuth, trigger, and publishing requirements are separate from this API-key connection check.

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Next steps

API keys

Create and manage scoped credentials.

Postman collections

Try the connection request in the matching API collection.