Migrating From Transactional Email to Agent Accounts

Nylas has introduced Agent Accounts, a beta feature that provides full hosted mailboxes with send and receive capabilities, threading, webhooks, and folders for AI agents that need to hold conversations. The solution addresses the fundamental limitation of transactional email providers like SendGrid and Resend, which only support one-way outbound messaging and cannot handle replies from prospects. Agent Accounts enable developers to create a mailbox with a single API call, automatically receive replies via webhooks, and maintain conversation context through thread IDs.

This is what most agent email code looks like today: // SendGrid / Resend / Postmark — outbound only await sendgrid.send { to: "prospect@example.com", from: "outreach@yourcompany.com", subject: "Following up on your demo request", html: "<p Hi Alice — wanted to follow up on...</p ", } ; // That's it. If Alice replies, the agent never sees it. The send works fine. The problem is everything after: when Alice replies, that reply bounces, lands at a no-reply nobody reads, or hits a human inbox the agent can't reach programmatically. The agent is talking into a void. Transactional providers were built for receipts and password resets — one-way mail — and an agent that's supposed to hold a conversation needs a receive path those APIs simply don't have. Agent Accounts https://developer.nylas.com/docs/v3/agent-accounts/ a beta feature from Nylas close that gap with a full hosted mailbox: send and receive, with threading, webhooks, and folders built in. Here's what the migration actually involves. Outbound barely changes — it's still an API call. The new parts are everything transactional providers never gave you: | Concern | Transactional provider | Agent Account | |---|---|---| | Outbound | API call | Same — POST /messages/send | | Inbound | None or polling a shared inbox | Replies land automatically, fire message.created | | Threading | You track Message-ID yourself | Headers preserved, threads grouped automatically | | Reply detection | Parse forwards, poll | Webhook within seconds of arrival | | DNS | SPF/DKIM/DMARC for the provider | MX, SPF, DKIM, DMARC for the mailbox host | One call creates the account; the response includes a grant id that identifies it on every later request: curl --request POST \ --url "https://api.us.nylas.com/v3/connect/custom" \ --header "Authorization: Bearer $NYLAS API KEY" \ --header "Content-Type: application/json" \ --data '{ "provider": "nylas", "settings": { "email": "outreach@agents.yourcompany.com" } }' Or nylas agent account create outreach@agents.yourcompany.com from the CLI. Custom domains need MX and TXT records pointed at the mail host before inbound works — provisioning docs here https://developer.nylas.com/docs/v3/agent-accounts/provisioning/ — but a .nylas.email trial subdomain works instantly for prototyping. The replacement send is nearly identical to what you had, with one addition that matters: store the thread id from the response. js const sent = await nylas.messages.send { identifier: AGENT GRANT ID, requestBody: { to: { email: "prospect@example.com", name: "Alice" } , subject: "Following up on your demo request", body: "<p Hi Alice — wanted to follow up on...</p ", }, } ; await db.conversations.create { threadId: sent.data.threadId, contactEmail: "prospect@example.com", step: "awaiting reply", } ; That stored ID is how you'll recognize Alice's reply when it comes back. Subscribe a webhook to message.created — this is the entire piece of infrastructure your transactional setup never had: curl --request POST \ --url "https://api.us.nylas.com/v3/webhooks" \ --header "Authorization: Bearer $NYLAS API KEY" \ --header "Content-Type: application/json" \ --data '{ "trigger types": "message.created" , "webhook url": "https://youragent.example.com/webhooks/nylas" }' The notification fires within seconds of a reply arriving. The handler then closes the loop that didn't exist before: look up the thread, skip the agent's own outbound, fetch the full body, restore context. js app.post "/webhooks/nylas", async req, res = { res.status 200 .end ; const event = req.body; if event.type == "message.created" return; const msg = event.data.object; if msg.grant id == AGENT GRANT ID return; // Skip the agent's own outbound messages. if msg.from?. 0 ?.email === "outreach@agents.yourcompany.com" return; // Is this a reply to something we sent? const conversation = await db.conversations.findByThreadId msg.thread id ; if conversation return; // new inbound, not a tracked reply // The webhook payload is a summary — fetch the full body. const full = await nylas.messages.find { identifier: AGENT GRANT ID, messageId: msg.id, } ; // Hand it to the LLM with conversation context restored. await processReply full.data, conversation ; } ; When the agent answers, pass reply to message id and the reply threads correctly in the recipient's client — Nylas sets the In-Reply-To and References headers, so there's no Message-ID bookkeeping on your side. And the recipient sees a normal threaded reply: no "sent via" branding, no relay footer. The reply-handling recipe https://developer.nylas.com/docs/cookbook/agent-accounts/handle-replies/ has the full routing logic. If your company's mail lives on Google Workspace or Microsoft 365, leave those MX records alone. The pattern that works: yourcompany.com pointed where it is. agents.yourcompany.com and point This also isolates the agent's sender reputation from your primary domain — which you'll care about the first time an experiment goes sideways. Does Nylas manage my conversation state too? No — and the comparison table above is honest about this. The Threads API gives you conversation history for free, but the mapping from threads to your agent's workflow state awaiting reply, confirmed, closed is still yours to build. That's the db.conversations table in the code above. Do I still need to generate Message-ID values? No. With a transactional provider, threading is your problem: you track Message-ID yourself and set In-Reply-To on every send. With an Agent Account, headers are preserved and messages group into threads automatically — reply to message id is the only threading concept your code touches.Keep the transactional provider for receipts and password resets if it's working — those flows don't need replies. Move only the conversations where the agent must see what comes back: outreach, support, scheduling, anything multi-turn. Different addresses, different jobs. The complete walkthrough is in the migration recipe https://developer.nylas.com/docs/cookbook/agent-accounts/migrate-from-transactional-email/ . Next step if you're tempted: provision a trial-subdomain account, re-point one send call at it, and reply to the email it sends you. Watching your own reply arrive as a webhook is the moment the architecture clicks.