mailplus_send_message

THE RISK

Medium Risk

Why mailplus_send_message needs a policy

Sending email is a Write operation—it creates new data (message records) and modifies server state reversibly. While emails cannot be truly unsent after delivery, the tool itself performs a creation/modification action rather than deletion or financial transaction.

From the tool's definition Tool name 'mailplus_send_message' and description 'Send an email via Synology MailPlus' indicate the tool creates and transmits new email messages. The requirement 'confirm=true to execute' suggests a confirmation guard is in place.

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

POLICY

How to control mailplus_send_message

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

policy.json

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

mailplus_send_message 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 Synology Office — 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 Synology Office tools

Destructive calendar_delete_event Delete a Synology Calendar event permanently. Requires confirm=true. Destructive drive_delete_file Delete a file or folder in Synology Drive (moves to trash by default). Set confirm=true to Destructive spreadsheet_delete_file WARNING: Permanently delete an ENTIRE spreadsheet file (.osheet). Destructive spreadsheet_delete_sheet Delete a sheet tab from a Synology Spreadsheet. This action cannot be undone. Provide eith Write spreadsheet_append_rows Append rows to the end of existing data in a Synology Spreadsheet sheet. Provide either fi Write drive_get_sharing_link Generate or retrieve a sharing link for a Synology Drive file with configurable permission Write calendar_create_calendar Create a new Synology Calendar. Write calendar_create_event Create a new Synology Calendar event. Requires confirm=true.

All 39 Synology Office tools →

Write tools on other servers

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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 mailplus_send_message

What does the mailplus_send_message tool do? +

Send an email via Synology MailPlus. Requires confirm=true to execute. It is categorised as a Write tool in the Synology Office MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on mailplus_send_message? +

Register the Synology Office MCP server in PolicyLayer and add a rule for mailplus_send_message: 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 Synology Office. Nothing to install.

What risk level is mailplus_send_message? +

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

Can I rate-limit mailplus_send_message? +

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

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

mailplus_send_message is provided by the Synology Office MCP server (vocweb/synology-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 Synology Office tool call.

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

CHECK YOUR STACK →