---
title: "What is MCP (Model Context Protocol)?"
description: "MCP is the open protocol that lets an AI agent call another product's tools. In direct mail it builds audiences and drafts copy for human approval."
canonical: https://trysincerely.com/glossary/mcp
last_updated: 2026-10-11
---
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# What is MCP (Model Context Protocol)?

> MCP is the open protocol that lets an AI agent call another product's tools. In direct mail it builds audiences and drafts copy for human approval.

Source: https://trysincerely.com/glossary/mcp

MCP (Model Context Protocol) is an open standard that lets an AI agent call another product's tools directly, instead of a person copying data between windows or a developer writing glue code for every integration. Anthropic introduced it in late 2024, and the major agent clients now speak it. An agent connected to a direct mail platform over MCP can build an audience, check addresses, and draft pieces, then hand a person the decision to send.

![A lilac agent node flows into a card of tool calls (query the CRM, verify addresses, draft 12 notes), then a gold card held for your click with a send button, then a stack of postcards to print.](https://trysincerely.com/images/glossary/mcp.webp)

*Over MCP an agent can query, verify and draft on its own, but a good direct mail server holds every send for a person's click.*

## Why it matters

Before MCP, giving an agent access to a product meant a custom integration: read the REST docs, manage an API key, write and maintain the code that translates between the model and the endpoints. MCP replaces that with one protocol. The client registers itself with the server, the person signs in through OAuth, and the agent receives tools it can call with the same authority that person already has, and no more.

Direct mail raises the stakes on that arrangement. Most MCP tools read and write data that can be corrected later. A tool that sends mail spends money on a call that cannot be taken back once a print vendor accepts the piece. So for mail, the definition of a good MCP server includes what it refuses: consequential calls should stop at a confirmation a human has to click, enforced by the server rather than requested in the prompt.

## Example

You tell Claude Code to write to the 12 accounts that went quiet since March. Over MCP, the agent queries your CRM sync, verifies each mailing address, and drafts 12 individual notes. Then it stops. A confirmation card lists the recipients, the design, and the price, and only your click releases the pieces to print.

What that looks like in practice is covered in [physical mail MCP](https://trysincerely.com/guides/physical-mail-mcp), and the connection steps live in [how to send direct mail from your AI agent](https://trysincerely.com/integrations/mcp-agents).

MCP gives the agent hands. The confirmation gate decides what those hands are allowed to hold.

## Main guide

- [Direct mail API](https://trysincerely.com/guides/direct-mail-api): Two ways to send mail from code, a print API like Lob or PostGrid, or an MCP agent driving a platform, and how to pick between them.

## Related questions

- [How to send direct mail from your AI agent](https://trysincerely.com/integrations/mcp-agents): Claude, Codex, Cursor, Hermes, or any MCP agent can build an audience, draft a piece, and request a send through Sincerely. A human confirms first.
- [Send physical mail from Claude](https://trysincerely.com/integrations/claude-mcp): Connect Claude to Sincerely and send real B2B direct mail. Claude Code takes one command, claude.ai takes a connector, and a human confirms every print.
- [Send physical mail from Grok](https://trysincerely.com/integrations/grok): Grok connects to Sincerely through a custom MCP connector on web, iOS, or Android. It drafts B2B mail a human confirms before anything prints.

---

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