Send & Receive Emails with Sim

Sim is a visual workspace for building AI agent workflows, block by block on a canvas. AgentMail is built in as a block: give it your API key and pick an operation. You will build a workflow that sends email from its own inbox, reads what comes back, and runs on its own when a new email arrives.

0. Prerequisites

You need an AgentMail API key and a Sim workspace. Generate the key from the AgentMail Console, or follow the Quickstart if this is your first AgentMail project.

Store the key once in Sim so it stays out of your saved workflows. Go to Settings > Secrets and add two entries:

Any block field can reference these with double curly braces, like {{AGENTMAIL_API_KEY}}. Sim resolves the value at run time and masks it in the run logs.

1. Add the AgentMail block

Open a workflow and drag an AgentMail block onto the canvas. Set its API Key field to {{AGENTMAIL_API_KEY}} and pick an Operation. The block’s remaining fields change to match the operation you picked.

Rename the block before you reference it anywhere. Sim names new blocks automatically, and downstream blocks read an output through a connection tag that starts with the block’s name: a block named SendEmail reads as <SendEmail.threadId>. Type < in any field to pick from the outputs of earlier blocks instead of typing tags by hand.

2. Test sending emails

The workflow needs an inbox to send from. If your organization already has one, put its inboxId in the AGENTMAIL_INBOX_ID secret and skip ahead to the send. Otherwise, create the inbox on the canvas: add an AgentMail block named CreateInbox, fill it in, and click Run.

The block’s output shows the new inbox’s inboxId plus its email address, like faircost773@agentmail.to. Put the inboxId in the AGENTMAIL_INBOX_ID secret so every later block can reference it.

Now send an email to an address you already check. Add an AgentMail block named SendEmail, fill it in, and click Run. The email should turn up there moments later, from your agent’s address.

To, CC, and BCC each take a comma-separated string when there is more than one recipient. The output exposes the sent message’s messageId and the threadId of the conversation it starts. Later blocks read them as <SendEmail.messageId> and <SendEmail.threadId> to follow up in the same thread.

3. Test receiving emails

From your everyday account, send an email to your agent’s address. Give it a subject and a line of text.

Add an AgentMail block named FetchEmails and run it. Your email should be the first item in the output’s messages array. Messages come back newest first, and a sent email typically arrives in about two seconds.

Each item carries a short preview of the body and the messageId you need to read the rest. To process full bodies, loop over the list:

1. Add a Loop block set to ForEach, with Collection set to <FetchEmails.messages>.
2. Inside the loop, add an AgentMail block with Operation set to Get Message, the same Inbox ID, and Message ID set to <loop.currentItem.messageId>.

Get Message returns each message’s full text and html, which is what you feed an Agent block. When the list is empty, the loop body is skipped and the workflow continues. To run all of this on a timer, for a morning digest for example, swap the Start trigger for a Schedule trigger and deploy the workflow. The schedule only runs once the workflow is deployed.

4. Trigger a workflow when email arrives

Polling on a schedule fits digests. For an agent that answers each email, point an AgentMail webhook at a Sim Webhook trigger instead.

In Sim:

1. Add the Webhook trigger as the workflow’s entry point.
2. Turn on Require Authentication and set a token, so only AgentMail can start the workflow.
3. Deploy the workflow. The webhook URL only accepts requests once the workflow is deployed.
4. Copy the webhook URL Sim generated.

Then register that URL with AgentMail. The headers map carries your Sim token, and AgentMail sends those headers with every delivery:

curl -X POST "https://api.agentmail.to/v0/webhooks" \
  -H "Authorization: Bearer $AGENTMAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "url": "<your Sim webhook URL>",
    "event_types": ["message.received"],
    "inbox_ids": ["faircost773@agentmail.to"],
    "headers": { "Authorization": "Bearer <your Sim trigger token>" }
  }'

If you left Require Authentication off, drop headers. Omit inbox_ids and the workflow runs for received mail across all your inboxes. One webhook watches at most 10 inboxes.

{
  "organization_id": "1a2b3c4d-5e6f-4a1b-8c2d-3e4f5a6b7c8d",
  "webhook_id": "ep_1a2b3c4d5e6f7a8b9c0d1e2f3a4",
  "url": "<your Sim webhook URL>",
  "event_types": ["message.received"],
  "inbox_ids": ["faircost773@agentmail.to"],
  "secret": "whsec_1a2b...c6d",
  "enabled": true,
  "created_at": "2026-08-25T09:00:00Z",
  "updated_at": "2026-08-25T09:00:00Z"
}

Save the webhook_id. You need it to update or delete this subscription later.

Send an email to the inbox from your everyday account. The run appears in Sim’s Logs, and the event payload is available to the blocks after the trigger by field name. The delivery carries the received message and its thread, so the subject reads as <webhook.message.subject> and the body as <webhook.message.text>. Wire a Reply to Message block with Inbox ID <webhook.message.inbox_id> and Message ID <webhook.message.message_id>, and the workflow answers in the original thread. Payload shapes, delivery retries, and signature verification are covered in Webhooks.

5. Operations reference

The walkthrough used five operations. The block covers the full AgentMail surface across messages, threads, inboxes, and drafts. Every operation authenticates with the API Key field, so {{AGENTMAIL_API_KEY}} works everywhere. The full parameter tables for every operation are in Sim’s AgentMail block reference.

Messages

Threads

Inboxes

Drafts

Next Steps