Reply to an existing email
AI agents use outlook_reply_to_email to create or update resources in Outlook — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Outlook environment.
This tool sends a reply to an existing email, which is a write operation that creates and sends a new message. It is high severity because an AI agent could send unintended or malicious replies on behalf of the user to real recipients, potentially causing reputational or operational harm.
From the tool's definition Reply to an existing email
Documented attack patterns abuse exactly the kind of access outlook_reply_to_email gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Outlook, and nothing reaches the server without passing your rules. This is the rule we recommend for outlook_reply_to_email:
{
"version": "1",
"default": "deny",
"tools": {
"outlook_reply_to_email": {
"limits": [
{
"counter": "outlook_reply_to_email_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}outlook_reply_to_email 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.
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Reply to an existing email. It is categorised as a Write tool in the Outlook MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Outlook MCP server in PolicyLayer and add a rule for outlook_reply_to_email: 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 Outlook. Nothing to install.
outlook_reply_to_email is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the outlook_reply_to_email 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 outlook_reply_to_email. 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.
outlook_reply_to_email is provided by the Outlook MCP server (xenoxilus/outlook-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Outlook, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
43 Outlook tools catalogued and risk-classified — across an index of 43,000+ MCP servers.