Submit a document for printing and postal mailing by the facility. Supported formats: PDF, DOCX, JPG, PNG, TXT, CSV. The document is stored securely and printed by the facility operator. IMPORTANT: With a production key (sk_agent_), this immediately charges the member's card on file. Use dry_run=...
Risk signalsHigh parameter count (28 properties)
Part of the Mailbox server.
Free to start. No card required.
AI agents use send_outbound_mail to create or modify resources in Mailbox. 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_outbound_mail 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 Mailbox.
Write tools can modify data. A rate limit prevents runaway bulk operations from AI agents.
{
"version": "1",
"default": "deny",
"tools": {
"send_outbound_mail": {
"limits": [
{
"counter": "send_outbound_mail_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}See the full Mailbox policy for all 29 tools.
These attack patterns abuse exactly the kind of access send_outbound_mail 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.
Submit a document for printing and postal mailing by the facility. Supported formats: PDF, DOCX, JPG, PNG, TXT, CSV. The document is stored securely and printed by the facility operator. IMPORTANT: With a production key (sk_agent_), this immediately charges the member's card on file. Use dry_run=true to preview cost before committing, or requires_approval=true to defer until human approval. Sandbox keys (sk_agent_test_) skip billing entirely. Optionally attach the outbound mail to inbound context with inbound_capture_id and postal_mail_thread_id so lineage stays explicit.. It is categorised as a Write tool in the Mailbox MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mailbox MCP server in PolicyLayer and add a rule for send_outbound_mail: 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 Mailbox. Nothing to install.
send_outbound_mail 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_outbound_mail 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_outbound_mail. 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_outbound_mail is provided by the Mailbox MCP server (https://mailbox.bot/api/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 29 Mailbox tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
4,600+ MCP servers and 31,000+ tools scanned and risk-classified.