AI agents use create_calendar_event 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.
This tool creates calendar events, which is a write operation—it adds new data to the user's calendar. While reversible (events can be deleted or modified), calendar events can have broader impacts if created maliciously (e.g., scheduling fake meetings, cluttering calendars, or creating false commitments).
From the tool's definition Tool name 'create_calendar_event' and description 'Create a new calendar event' indicate creation of new data in a calendar system. This is a write operation that adds data reversibly (events can be modified or deleted).
Documented attack patterns abuse exactly the kind of access create_calendar_event 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 create_calendar_event:
{
"version": "1",
"default": "deny",
"tools": {
"create_calendar_event": {
"limits": [
{
"counter": "create_calendar_event_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}create_calendar_event 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.
Free to start. No card required.
Create a new calendar event. 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 create_calendar_event: 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.
create_calendar_event 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 create_calendar_event 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 create_calendar_event. 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.
create_calendar_event 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.
Free to start. No card required.
38 Fastmail MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.