letterport

Real inboxes for AI agents.

Create an email address with one API call. Mail sent to it arrives as clean JSON your agent can read: the sender, the new text of a reply without the quoted history, the thread it belongs to, and its attachments.

Request early access How we keep mail clean
Arrives at research@letterport.dev
From: Maya Chen <maya@example.com>
To: research@letterport.dev
Subject: Re: Supplier quote for Q4
Message-ID: <CAH7x9q4@mail.example.com>
In-Reply-To: <0100019a5e@email.amazonses.com>
Content-Type: multipart/mixed

Quote attached, 40 units as agreed.

On Mon, research@letterport.dev wrote:
> Could you send the updated quote?
[quote.pdf, 84 KB]
What your agent reads
{
  "from": {
    "address": "maya@example.com",
    "name": "Maya Chen"
  },
  "subject": "Re: Supplier quote for Q4",
  "extracted_text":
    "Quote attached, 40 units as agreed.",
  "thread_id": "thr_01a15de9ffec…",
  "attachments": [
    { "filename": "quote.pdf",
      "content_type": "application/pdf" }
  ]
}

How it works

An inbox is a real address on letterport.dev. Our mail servers receive for it, scan for spam and viruses, and keep each message for your agent to read through the API.

  1. Create an inbox

    Pick a name, or leave it out and get a generated one. The address works at once.

    API=https://api.letterport.dev/v1
curl "$API/inboxes" \
  -H "Authorization: Bearer $KEY" \
  --json '{"local_part":"research"}'

  2. Mail arrives

    Anyone can write to research@letterport.dev. Replies are grouped into threads by their headers, never by subject alone. 

    From: maya@example.com
To:   research@letterport.dev

  3. Your agent reads it

    Fetch new messages, a whole thread, or an attachment. Filter by sender, subject and date.

    curl "$API/inboxes/$ID/messages" \
  -H "Authorization: Bearer $KEY"

What works today

letterport is in early access. This is exactly what is running now, and what comes next.

Capability Status Details
Inboxes on letterport.dev Live Create, rename, pause and delete addresses through the API. A deleted address is never reissued.
Receiving mail Live Spam and virus scanning, HTML made safe, attachments kept privately, replies threaded.
Reading over REST Live Messages, threads and attachments, with API keys you can limit to one inbox.
Sending and replying Next From your agent's own address, under the mail rules below.
Webhooks, MCP server, agent skill Next Be told when mail arrives; connect Claude Code and other agents directly.
Your own domain Later Addresses like support@agents.yourcompany.com, on paid plans.

Mail rules

Agents should hold conversations, not run campaigns. Every account sends under these rules, and paying doesn't lift them. The full text is our acceptable use policy.

  • Conversations and transactional mail only

    Replies, follow-ups, confirmations and notifications people expect. No bulk mail, marketing, newsletters or cold outreach.

  • New accounts start restricted

    A new account can send only to recipients it has verified, until it has established normal use.

  • Limits count recipients

    The free plan allows 50 recipients a day and 1,000 a month across all of an account's inboxes. To, Cc and Bcc each count.

  • Bounces and complaints stop mail

    Addresses that bounce or complain are suppressed automatically. Accounts with high bounce or complaint rates are paused and reviewed.

  • Every message is authenticated

    Mail goes out from the agent's own address, signed with DKIM and aligned with SPF and DMARC.

  • Abuse reports are read

    Write to abuse@letterport.dev. We investigate every report and suspend accounts that break these rules.

Pricing

Start free on letterport.dev. Paid plans with your own domain come with our public launch.

Free

$0 no card needed

  • 3 inboxes on letterport.dev
  • 50 recipients a day, 1,000 a month
  • Receiving and the full read API

Paid

Soon priced at launch

  • Your own domain or subdomain
  • More inboxes and higher limits
  • Everything in Free