Multichannel messaging for AI agents

Someone who subscribed to your newsletter has not agreed to receive WhatsApp messages from you. In most jurisdictions that is a legal distinction, and in every jurisdiction it is a trust one. A contact carries an identity and a consent record per channel, and a send to a channel without consent is refused rather than delivered.

This is the part an agent will get wrong if you leave it to judgement: it sees a phone number in the contact and treats it as reachable.

send_message {
  channel: "whatsapp",
  to: "+393331234567",
  templateId: "order-shipped",
  variables: { order: "4182" }
}

Same shape for all three, with the addressing each one needs: an email address, an E.164 number, a chat id. Outside the 24 hour window WhatsApp needs an approved template rather than free text, which is a Meta rule and not ours.

{ "id": "m1", "type": "message",
  "preferredChannel": "email",
  "fallbackChain": ["email", "whatsapp"],
  "templateByChannel": { "email": "<uuid>", "whatsapp": "<uuid>" },
  "next": "w2" }

The node declares a preferred channel and a chain to fall back through. The worker resolves the contact's identities and consent at that moment and picks the first channel that is actually available, so the decision is made against the state of the world rather than the model's memory of it.

Put a wait before the fallback. Falling back the instant an email is accepted means you are paying for a WhatsApp message to someone who was about to read the email.

A WhatsApp template message costs materially more than an email, and the difference is per message. On ten thousand contacts, a fallback that fires too early is a bill you did not plan and a channel you have taught people to ignore. The cheapest correct answer is usually email first, with the paid channel reserved for what is time critical.

WhatsApp and Telegram need credentials from those platforms and, for WhatsApp, templates approved by Meta. We can orchestrate them; we cannot make that approval faster. If your use case is a single transactional email, none of this matters and a transactional-only provider will serve you fine.