receive_custom_message

THE RISK

Medium Risk

Why receive_custom_message needs a policy

This tool writes a new custom message to a channel in Frontapp. It creates data (a message) within the platform. While 'receive' sounds passive, in the context of Frontapp's API this refers to injecting/posting an inbound custom message into a channel, which is a reversible write operation. Severity is medium as misuse could flood channels with unwanted messages or impersonate inbound communications.

From the tool's definition 'Receive a custom message on a channel' — creates/posts a new message into a channel

Documented attack patterns abuse exactly the kind of access receive_custom_message gives an agent:

POLICY

How to control receive_custom_message

PolicyLayer is an MCP gateway — it sits between your AI agents and Frontapp MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for receive_custom_message:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "receive_custom_message": {
      "limits": [
        {
          "counter": "receive_custom_message_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

receive_custom_message stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register Frontapp MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

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All 151 Frontapp MCP Server tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about receive_custom_message

What does the receive_custom_message tool do? +

Receive a custom message on a channel. It is categorised as a Write tool in the Frontapp MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on receive_custom_message? +

Register the Frontapp MCP Server MCP server in PolicyLayer and add a rule for receive_custom_message: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Frontapp MCP Server. Nothing to install.

What risk level is receive_custom_message? +

receive_custom_message is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit receive_custom_message? +

Yes. Add a rate_limit block to the receive_custom_message rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block receive_custom_message completely? +

Set action: deny in the PolicyLayer policy for receive_custom_message. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides receive_custom_message? +

receive_custom_message is provided by the Frontapp MCP Server MCP server (zqushair/frontapp-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Frontapp MCP Server tool call.

Start from Frontapp MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →