Reply to message
Risk signalsAccepts raw HTML/template content (html) · Accepts file system path (attachments[].filename) · Accepts URL/endpoint input (attachments[].url) · High parameter count (11 properties)
Part of the Agentmail server.
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AI agents call reply_to_message to retrieve information from Agentmail without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though reply_to_message only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"reply_to_message": {}
}
}See the full Agentmail policy for all 11 tools.
These attack patterns abuse exactly the kind of access reply_to_message gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
Reply to message. It is categorised as a Read tool in the Agentmail MCP Server, which means it retrieves data without modifying state.
Register the Agentmail MCP server in PolicyLayer and add a rule for reply_to_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 Agentmail. Nothing to install.
reply_to_message 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 reply_to_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.
Set action: deny in the PolicyLayer policy for reply_to_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.
reply_to_message is provided by the Agentmail MCP server (agentmail-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 11 Agentmail tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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