AI agents use send_batch to create or modify resources in Postmark. Write operations carry medium risk because an autonomous agent could trigger bulk unintended modifications. Rate limits prevent a single agent session from making hundreds of changes in rapid succession. Argument validation ensures the agent passes expected values.
Without a policy, an AI agent could call send_batch repeatedly, creating or modifying resources faster than any human could review. PolicyLayer's rate limiting ensures write operations happen at a controlled pace, and argument validation catches malformed or unexpected inputs before they reach Postmark.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"send_batch": {
"limits": [
{
"counter": "send_batch_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Postmark policy for all 30 tools.
These attack patterns abuse exactly the kind of access send_batch gives an agent. Each links to the full case and the policy that stops it:
Other write tools across the catalogue. The same approach applies to each: rate-limit and validate the arguments.
Send up to 500 emails.. It is categorised as a Write tool in the Postmark MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Postmark MCP server in PolicyLayer and add a rule for send_batch: 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 Postmark. Nothing to install.
send_batch 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 send_batch 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 send_batch. 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.
send_batch is provided by the Postmark MCP server (https://gateway.pipeworx.io/postmark/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 30 Postmark tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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