flag_emails

THE RISK

Medium Risk

Why flag_emails needs a policy

Flagging emails modifies their state (adds a flag/star marker) but is reversible — the sibling tool 'unflag_emails' exists to undo this action. This is a metadata write operation with no destructive or financial consequences. Misuse could clutter or mislabel a user's inbox but blast radius is low-to-medium.

From the tool's definition Flag emails as important/starred using UIDs

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

POLICY

How to control flag_emails

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

policy.json

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

flag_emails 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 Yahoo Mail — 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 Yahoo Mail tools

Destructive delete_emails Move emails to Trash folder using UIDs (soft delete, recoverable). UIDs are permanent iden Write unflag_emails Remove flag/star from emails using UIDs. UIDs are permanent identifiers. Write archive_emails Move emails to Archive folder using UIDs for long-term storage. UIDs are permanent identif Write mark_as_read Mark emails as read using UIDs. UIDs are permanent identifiers. Write mark_as_unread Mark emails as unread using UIDs. UIDs are permanent identifiers. Write move_emails Move emails to a specified folder using UIDs. UIDs are permanent identifiers. Use list_fol Read list_emails List recent emails from a Yahoo Mail folder. Returns UIDs (permanent identifiers) and enri Read list_folders List all available IMAP folders/mailboxes in your Yahoo Mail account

All 11 Yahoo Mail 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 flag_emails

What does the flag_emails tool do? +

Flag emails as important/starred using UIDs. UIDs are permanent identifiers. It is categorised as a Write tool in the Yahoo Mail MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on flag_emails? +

Register the Yahoo Mail MCP server in PolicyLayer and add a rule for flag_emails: 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 Yahoo Mail. Nothing to install.

What risk level is flag_emails? +

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

Can I rate-limit flag_emails? +

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

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

flag_emails is provided by the Yahoo Mail MCP server (jtokib/yahoo-mail-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Yahoo Mail tool call.

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

CHECK YOUR STACK →