send_mail · Tbird MCP: Risk & Policy

WHAT IT DOES

What send_mail does on Tbird

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

WHY IT NEEDS A POLICY

Why send_mail needs a policy

This tool creates new email messages and modifies the Sent folder (writes records), which are reversible actions. Although email transmission can have external consequences, the tool itself performs data creation/modification rather than executing arbitrary code or deleting data.

From the tool's definition Tool name 'send_mail' combined with server description stating it 'sends mail via SMTP' and 'filing copies in Thunderbird's Sent folder' indicates creation of new messages and modification of mailbox state.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

send_mail Rate-limited

send_mail 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": {
    "send_mail": {
      "limits": [
        {
          "counter": "send_mail_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 Tbird, so you can run agents against it safely.

FAQ

Questions about send_mail

What does the send_mail tool do? +

send_mail. It is categorised as a Write tool in the Tbird MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on send_mail? +

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

What risk level is send_mail? +

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

Can I rate-limit send_mail? +

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

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

send_mail is provided by the Tbird MCP server (neil-zielsdorf/tbird-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.