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How do I get an API key?

Sign up at openmail.sh and complete the setup wizard. See Quickstart for the full flow.

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What’s the base URL?

https://api.openmail.sh

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Can a user have multiple inboxes?

Yes. Use the same externalId (your user ID) when creating each inbox. Webhooks include external_id for routing and inbox_id so you know which inbox the message belongs to. Route to the user’s container by external_id; use inbox_id to identify the inbox (e.g. personal vs work).

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Do you support multi-tenant?

Yes. One platform account, many inboxes. Pass your user or container ID as externalId when creating each inbox; it comes back as external_id in every webhook so you can route to the right agent. No separate tenant abstraction — just create inboxes and route by external_id.

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How do webhooks work?

Configure a webhook URL in the Dashboard. When inbound email arrives, we POST a message.received event. See Overview and Setup.

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What’s the Idempotency-Key for?

The send endpoint requires it. Use a unique UUID per send so retries don’t create duplicate emails. See Idempotency.

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How do I handle attachments?

Inbound attachments include a signed URL in the payload. Fetch promptly; URLs expire. See Attachments.