List sending identities (email addresses that can be used for sending)
AI agents call list_identities 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 configuration data (available sender identities) from Fastmail. It performs a read-only lookup with no capability to modify identities, send emails, or trigger external operations. While identity information could inform social engineering if exposed to an attacker, the tool itself is purely informational and poses minimal risk in normal usage.
From the tool's definition Tool description states 'List sending identities' — a query operation that retrieves email addresses without modifying, deleting, or executing actions. No side effects or state changes.
Documented attack patterns abuse exactly the kind of access list_identities 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_identities:
{
"version": "1",
"default": "deny",
"tools": {
"list_identities": {}
}
}list_identities is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List sending identities (email addresses that can be used for sending). 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_identities: 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_identities 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_identities 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_identities. 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_identities 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.