AI agents use move_email to create or update resources in Fastmail MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fastmail MCP Server environment.
Moving emails between mailboxes is a write operation that modifies email metadata and organization state, but remains fully reversible. It does not delete data (would be Destructive), does not execute arbitrary code (would be Execute), and does not involve financial transactions (would be Financial).
From the tool's definition Tool description states 'Move an email to a different mailbox', which modifies the organizational state of email data by changing its location/folder assignment. This is a reversible modification operation (emails can be moved back).
Documented attack patterns abuse exactly the kind of access move_email 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 move_email:
{
"version": "1",
"default": "deny",
"tools": {
"move_email": {
"limits": [
{
"counter": "move_email_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}move_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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Move an email to a different mailbox. It is categorised as a Write tool in the Fastmail MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Fastmail MCP Server MCP server in PolicyLayer and add a rule for move_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 Fastmail MCP Server. Nothing to install.
move_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 move_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 move_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.
move_email 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.