AI agents call list_emails to retrieve information from Fastmail MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool retrieves and displays existing emails from a mailbox. There is no indication of creating, modifying, deleting, or executing operations. The action is purely informational. While emails may contain sensitive information, the severity is low because listing is a standard read operation with no destructive or financial impact.
From the tool's definition Tool name 'list_emails' and description 'List emails from a mailbox' indicate retrieval of email data without modification or deletion. This is a query operation with no side effects.
Documented attack patterns abuse exactly the kind of access list_emails gives an agent:
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 list_emails:
{
"version": "1",
"default": "deny",
"tools": {
"list_emails": {}
}
}list_emails is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List emails from a mailbox. It is categorised as a Read tool in the Fastmail MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Fastmail MCP Server MCP server in PolicyLayer and add a rule for list_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 Fastmail MCP Server. Nothing to install.
list_emails is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the list_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.
Set action: deny in the PolicyLayer policy for list_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.
list_emails 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.
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.
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38 Fastmail MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.