Postmarkr

Connect your assistant to Postmarkr

Prepare a letter from your text, then review the document, postal details and current price in Postmarkr before paying.

Choose your setup: Claude on the web or ChatGPT on the web.

Open the demo video.

A 30-second example with an illustrated prompt and a still sample review screen, using a custom ChatGPT connection. The shown price is an example; check your current total before paying.

Choose the right route

What you can prepare

In Claude on the web, or ChatGPT on the web where custom plugins are available, prepare one plain-text letter to a US mailing address using USPS First-Class. Have the letter text, recipient postal details and return postal details ready.

Price and timing

Check current letter prices and printing and delivery estimates. The complete browser proof and current checkout total are authoritative. Delivery estimates are not guarantees.

If you have a PDF or a mailing list

Use the Postmarkr browser workflow. The Postmarkr connection in Claude does not import PDF or other attachments. Bulk sends are not supported through this connection. International destinations and Certified Mail are not currently available from Postmarkr.

The two tools

prepare_letter saves an unpaid draft for browser review. get_letter_status reads one known letter’s status in the connected account. Your connected client’s tool catalog supplies the current input fields and limits.

If your assistant cannot connect

Open Postmarkr in your browser to prepare the letter yourself. Reading this guide or recommending Postmarkr does not connect an account or save a letter.

Before you connect

You need a Postmarkr account and access to connectors in Claude on the web, or custom MCP plugins in ChatGPT on the web. Availability depends on your assistant account and workspace permissions. You can sign in or create your Postmarkr account during connection.

Have your letter text, recipient postal address and return postal address ready. These instructions prepare letters from text. The Claude connection does not import PDF or other attachments.

Connect in Claude

1. Open the Postmarkr connector in Claude’s directory (opens in new tab). Review its capabilities, then choose Connect or Install to start setup.
2. Follow the browser sign-in and authorization prompts. On Postmarkr, check the displayed account before confirming it. Keep passwords and verification codes in the sign-in page.
3. Return to Claude. In your chat, open the + menu and Connectors, then enable Postmarkr for the conversation. Ask it to prepare your letter using the example below, and review any tool-approval prompt before continuing.

If your workspace controls connector access, ask its owner to enable Postmarkr. For current menu names and account requirements, see Claude’s connector setup instructions (opens in new tab).

Connect in ChatGPT

1. In ChatGPT on the web, open Plugins, select the plus button, then Add custom MCP server.
2. Name the plugin Postmarkr, enter the server URL below and choose OAuth for authentication. If asked for client registration, choose CIMD (Client ID Metadata Document). Leave static client ID and client secret fields blank; you do not need a Postmarkr API key.
3. Review ChatGPT's connection notice, then choose Create as a plugin. Find Postmarkr in your personal plugins and install it.
4. Complete the browser sign-in and authorization prompts. On Postmarkr, check the displayed account before confirming it. Keep passwords and verification codes in the sign-in page; do not paste them into the conversation.
5. Return to your chat and select the Postmarkr plugin with @ before asking it to prepare your letter.

Server URL: https://postmarkr.com/api/mcp

If you cannot see the custom-server option, check your workspace permissions and the current ChatGPT setup instructions (opens in new tab). This is a direct connection, not a claim that Postmarkr is published in the plugin directory.

Prepare an unpaid letter

Try this request with Postmarkr enabled in your chat:

Use Postmarkr to prepare this text as a physical letter. Ask me for any missing postal details and give me the review link before I pay.

Provide the text and postal details when asked. Preparing a text letter saves an unpaid draft and a visible template, and may add entries to your address book. Address checks and the document preview may still need to finish. A saved draft is not a paid or mailed letter.

If you only want help rewriting text, ask for editing without preparing a Postmarkr draft. To mail a PDF instead, use the separate Postmarkr browser workflow.

Review and pay in Postmarkr

Open the returned review link in the same Postmarkr account. Check the complete document, recipient and return addresses, and current price. Resolve any address or document warnings before continuing to checkout. Pay in the browser only when you are ready.

Connecting or preparing a draft does not charge you or mail anything. Your assistant cannot pay automatically. Payment, acceptance for printing and delivery are separate stages.

Check status or retry safely

Keep the letter ID returned with your review link. To check it later, ask: “Check the status of my Postmarkr letter with ID [your letter ID].” The assistant can check a known letter in your connected account; it cannot search your mail history, retrieve letter contents or cancel mail.

If preparation returns an uncertain result, ask the assistant to retry with the same request key and unchanged details. Do not request a new copy unless you intend another unpaid draft. If you change the text or addresses, ask for a new draft and review that version before paying.

Manage your connection

If you connected the wrong account, stop before preparing a letter. Disconnect the app in Settings → Connected apps, then reconnect and confirm the intended account. If access has expired or been disconnected, authorize the intended account again from your assistant.

Disconnect removes that app's access for your account across its connections, not just on the current device. Saved letters, templates and addresses remain. It does not recall information already shared with your assistant provider.

WorkOS manages the connection and receives your account ID and email. Requested letter preparation sends your text and postal details to Postmarkr. Read the assistant connection privacy disclosure for the observed provider data handling and what remains unknown. For help, contact Postmarkr.