AI agents call get_thread 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.
This tool retrieves and queries email conversation data without making any changes to the underlying data. It has no side effects beyond reading what already exists in the user's mailbox. The blast radius of misuse is minimal—an attacker could read emails they shouldn't access, but cannot modify, delete, send, or perform financial transactions.
From the tool's definition Tool name 'get_thread' and description 'Get all emails in a conversation thread' indicate retrieval of existing data with no modification, deletion, or side effects.
Documented attack patterns abuse exactly the kind of access get_thread 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 get_thread:
{
"version": "1",
"default": "deny",
"tools": {
"get_thread": {}
}
}get_thread is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get all emails in a conversation thread. 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 get_thread: 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.
get_thread 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 get_thread 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 get_thread. 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.
get_thread 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.