add_labels

THE RISK

Medium Risk

Why add_labels needs a policy

Adding labels to emails is a reversible modification operation that organizes data without side effects beyond the intended label change. It does not execute external commands, delete data, move money, or trigger destructive actions. While it modifies state, labels can be removed, making this a Write category tool.

From the tool's definition Tool description states 'Add labels (mailboxes) to an email without removing existing ones' — this modifies email metadata/organization state reversibly by adding labels.

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

POLICY

How to control add_labels

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

policy.json

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

add_labels 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 Fastmail 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

More Fastmail MCP Server tools

Destructive bulk_delete Delete multiple emails (move to trash) Destructive delete_email Delete an email (move to trash) Write bulk_remove_labels Remove labels from multiple emails simultaneously Write remove_labels Remove specific labels (mailboxes) from an email Write reply_email Reply to an existing email with proper threading headers (In-Reply-To, References). Automa Write test_bulk_operations Test bulk operations by finding recent emails and performing safe operations (mark read/un Write bulk_add_labels Add labels to multiple emails simultaneously Write bulk_mark_read Mark multiple emails as read/unread

All 38 Fastmail MCP Server tools →

Write tools on other servers

M-Team MCP Server download_torrent YouTube MCP Server generate_video_title Android Forensics ADB MCP Server combine_reports 0xarchive web3_signup

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 add_labels

What does the add_labels tool do? +

Add labels (mailboxes) to an email without removing existing ones. It is categorised as a Write tool in the Fastmail 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 add_labels? +

Register the Fastmail MCP Server MCP server in PolicyLayer and add a rule for add_labels: 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 Fastmail MCP Server. Nothing to install.

What risk level is add_labels? +

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

Can I rate-limit add_labels? +

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

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

add_labels is provided by the Fastmail MCP Server MCP server (madllama25/fastmail-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Fastmail MCP Server tool call.

Start from Fastmail 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 →