reply_to_email · Mcp Mail Server MCP: Risk & Policy

WHAT IT DOES

What reply_to_email does on Mcp Mail Server

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

WHY IT NEEDS A POLICY

Why reply_to_email needs a policy

This tool sends an email reply via SMTP, which is a write/create operation — it creates a new outbound email message. While it cannot be 'undone' once sent, sending email is conventionally classified as Write (create/post) rather than Destructive.

From the tool's definition Reply to a specific email by UID. Automatically sets reply headers, adds Re: prefix, and includes original message.

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 Mcp Mail Server, so you can run agents against it safely.

FAQ

Questions about reply_to_email

What does the reply_to_email tool do? +

Reply to a specific email by UID. Automatically sets reply headers, adds Re: prefix, and includes original message. Auto-connects to both IMAP and SMTP if not already connected. It is categorised as a Write tool in the Mcp Mail 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 reply_to_email? +

Register the Mcp Mail Server 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 Mcp Mail Server. 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 Mcp Mail Server MCP server (mcp-mail-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.