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Mail by Pony

com.mailbypony/mail-by-pony in the official MCP registry. Endpoint https://www.mailbypony.com/mcp.

The registry describes it as: Print and mail real letters through USPS. Write, preview the exact printed proof, then pay or send.

We read its 39 tools on 2026-10-31. Nothing in them matched our tool-poisoning rules. It also sets server instructions, text a client puts in front of the model on connect; those were read too.

A clean read means these rules found nothing, not that the server is harmless. A server can change its tools at any time, which is why the index reads it again every week.

Connect it

The endpoint answers MCP over HTTP; that is how we read it. Add it to your client:

Claude Code

claude mcp add --transport http mail-by-pony https://www.mailbypony.com/mcp

Cursor: ~/.cursor/mcp.json

{
  "mcpServers": {
    "mail-by-pony": {
      "url": "https://www.mailbypony.com/mcp"
    }
  }
}

VS Code

code --add-mcp '{"name":"mail-by-pony","type":"http","url":"https://www.mailbypony.com/mcp"}'

Some servers ask you to sign in the first time a client connects, or want a key from the people who run them; the server's own docs say which.

Let Claude Code check servers as it adds them

With the free lazaretto-guard plugin installed, when Claude Code adds a server for you or writes one into an MCP config, the plugin reads the server's tools first and asks you if one of our rules matches. Install it, restart Claude Code, then ask it to run the command above.

Install lazaretto-guard

claude plugin marketplace add jamesdfinance-dev/lazaretto-plugins
claude plugin install lazaretto-guard@lazaretto-plugins

Tools it advertises

catalog ui_diagnostic list_drafts create_draft get_draft update_draft list_address_references upload_attachment add_library_artwork remove_attachment archive_draft preview quote prepare_checkout get_checkout_preparation checkout create_payment_link list_orders get_order reconcile_payment cancel_order request_status show_letter get_connection_identity get_proof get_credit_balance list_credit_transactions create_credit_topup get_credit_topup list_agent_grants quote_for_send send_with_credits create_template list_templates get_template delete_template create_template_draft create_batch get_batch

Tool changes

We compare every full read of this server with the one before. No change in what its tools say has been seen since we started keeping this record on 2026-10-30.

Fingerprint of its tools at our last full read (2026-10-31): 84e7f0bef83b1262. A client can hash the tools it is served the same way and compare; the full value and a hash per tool are in this page as JSON.

Run this server? Show the check in your README

The badge reflects the latest weekly read:

Markdown

[![MCP tool check](https://lazaretto.dev/mcp-registry/com-mailbypony-mail-by-pony/badge.svg)](https://lazaretto.dev/mcp-registry/com-mailbypony-mail-by-pony)

How this was checked

Lazaretto connects to the endpoint the way any MCP client does, asks the server to introduce itself and list its tools, and reads every name, description, parameter schema and server instruction for tool poisoning: hidden directive blocks, orders to read local secrets, parameters built to carry secrets or the conversation out, orders that redirect another server's tools, and invisible characters. It never calls a tool. What we found across the registry.

To run the same check every time Claude Code adds a server, install the free lazaretto-guard plugin. Browse every server in the index.