Email Threading That Keeps Agents in Context

import multimail

client = multimail.Client(api_key="$MULTIMAIL_API_KEY")

"cm"># Fetch the full thread — not just the latest message
thread = client.get_thread(thread_id="thrd_01HXYZ1234ABCD")

print(f"Subject: {thread.subject}")
print(f"Messages in thread: {len(thread.messages)}")

for msg in thread.messages:
    print(f"  [{msg.sent_at}] From: {msg.from_address}")
    print(f"  Message-ID: {msg.message_id}")
    print(f"  Preview: {msg.body_text[:120]}...")

"cm"># The last message is what we will reply to
latest = thread.messages[-1]
print(f"Replying to message: {latest.message_id}")

import multimail
from anthropic import Anthropic

client = multimail.Client(api_key="$MULTIMAIL_API_KEY")
anthropic = Anthropic()

"cm"># Load the thread
thread = client.get_thread(thread_id="thrd_01HXYZ1234ABCD")

"cm"># Build conversation history for the model
messages = []
for msg in thread.messages:
    role = "assistant" if msg.from_address == "[email protected]" else "user"
    messages.append({"role": role, "content": msg.body_text})

"cm"># Add the drafting instruction
messages.append({
    "role": "user",
    "content": "Draft a reply covering the deployment details and remaining action items from this thread."
})

"cm"># Draft the reply with full thread context
response = anthropic.messages.create(
    model="claude-sonnet-4-6",
    max_tokens=1024,
    system="You are an assistant drafting email replies. Be concise and address only what is new.",
    messages=messages
)
reply_body = response.content[0].text

"cm"># Send — threading headers set automatically
result = client.reply_email(
    thread_id=thread.thread_id,
    reply_to_message_id=thread.messages[-1].message_id,
    from_address="[email protected]",
    body_text=reply_body,
)

print(f"Sent: {result.message_id}")
print(f"Thread position: {result.position_in_thread} of {result.thread_length}")

"cm"># Step 1: Fetch the full thread
curl -s https://api.multimail.dev/v1/threads/thrd_01HXYZ1234ABCD \
  -H "Authorization: Bearer $MULTIMAIL_API_KEY" | jq .

"cm"># Response shape:
"cm"># {
"cm">#   "thread_id": "thrd_01HXYZ1234ABCD",
"cm">#   "subject": "Re: Next steps on your deployment",
"cm">#   "messages": [
"cm">#     { "message_id": "<[email protected]>", "from_address": "[email protected]", "body_text": "..." },
#     { "message_id": "<[email protected]>", "from_address": "[email protected]", "body_text": "..." }
#   ],
#   "participant_addresses": ["[email protected]", "[email protected]"]
# }

# Step 2: Reply — MultiMail sets In-Reply-To and References automatically
curl -s -X POST https://api.multimail.dev/v1/emails/reply \
  -H "Authorization: Bearer $MULTIMAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: reply-$(uuidgen)" \
  -d &"cm">#039;{
    "thread_id": "thrd_01HXYZ1234ABCD",
    "reply_to_message_id": "<[email protected]>",
    "from_address": "[email protected]",
    "body_text": "Following up on the prior thread, here are the deployment details we discussed and the remaining action items."
  }&"cm">#039; | jq .

// Tool: get_thread
// Available in Claude Desktop, Cursor, Windsurf, and any MCP client

Tool call: get_thread
Arguments:
  thread_id: "thrd_01HXYZ1234ABCD"

Returns:
  subject: "Re: Next steps on your deployment"
  messages: [ ... ordered list of all messages with bodies and Message-IDs ... ]
  participant_addresses: ["[email protected]", "[email protected]"]

---

// Tool: reply_email
// MultiMail sets In-Reply-To and References — do not construct headers manually

Tool call: reply_email
Arguments:
  thread_id: "thrd_01HXYZ1234ABCD"
  reply_to_message_id: "<[email protected]>"
  from_address: "[email protected]"
  body_text: "Following up on the prior thread, here are the deployment details we discussed and the remaining action items."

Returns:
  message_id: "<[email protected]>"
  position_in_thread: 3
  headers_set: ["In-Reply-To", "References"]

from fastapi import FastAPI, Request
import multimail

app = FastAPI()
client = multimail.Client(api_key="$MULTIMAIL_API_KEY")

@app.post("/webhooks/multimail")
async def handle_inbound(request: Request):
    payload = await request.json()

    "cm"># MultiMail resolves thread_id on inbound — no header parsing needed
    if payload["event"] != "email.inbound":
        return {"ok": True}

    thread_id = payload["thread_id"]
    message_id = payload["message_id"]

    "cm"># Load the full thread to give the agent complete context
    thread = client.get_thread(thread_id=thread_id)

    "cm"># Your agent processes the thread and drafts a reply
    reply_body = your_agent.process_thread(thread.messages)

    "cm"># Reply anchored to the triggering message
    client.reply_email(
        thread_id=thread_id,
        reply_to_message_id=message_id,
        from_address="[email protected]",
        body_text=reply_body,
    )

    return {"ok": True}