reply_to_email · Gmail MCP: Risk & Policy

WHAT IT DOES

What reply_to_email does on Gmail

AI agents use reply_to_email to create or update resources in Gmail — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Gmail environment.

WHY IT NEEDS A POLICY

Why reply_to_email needs a policy

This tool creates new messages reversibly (emails can be deleted or unsent in many cases). While it modifies Gmail state, it does not irreversibly delete data (Destructive), execute arbitrary code (Execute), or move money (Financial).

From the tool's definition Tool description states 'Reply to an existing email thread' and can 'include all CC recipients', indicating it creates new email messages and modifies email threads by adding replies.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

reply_to_email Rate-limited

reply_to_email 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.

View as policy code

policy.json

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

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Gmail, so you can run agents against it safely.

FAQ

Questions about reply_to_email

What does the reply_to_email tool do? +

Reply to an existing email thread. Set replyAll:true to include all CC recipients. It is categorised as a Write tool in the Gmail MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on reply_to_email? +

Register the Gmail MCP server in PolicyLayer and add a rule for reply_to_email: 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 Gmail. Nothing to install.

What risk level is reply_to_email? +

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

Can I rate-limit reply_to_email? +

Yes. Add a rate_limit block to the reply_to_email 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 reply_to_email completely? +

Set action: deny in the PolicyLayer policy for reply_to_email. 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 reply_to_email? +

reply_to_email is provided by the Gmail MCP server (ndungukamami-sketch/gmail-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.