Add a contact to a segment in Resend (by contact ID or email).
AI agents use add-contact-to-segment to create or update resources in Email Sending MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Email Sending MCP environment.
This tool creates or modifies data reversibly by adding a contact to a segment. It does not delete data (Destructive), execute arbitrary code (Execute), move money (Financial), or merely retrieve information (Read). The operation can be undone by removing the contact from the segment.
From the tool's definition The tool description states it 'Add a contact to a segment' in Resend, which is a modification operation that changes the state of a contact record (assignment to a segment).
Documented attack patterns abuse exactly the kind of access add-contact-to-segment gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Email Sending MCP, and nothing reaches the server without passing your rules. This is the rule we recommend for add-contact-to-segment:
{
"version": "1",
"default": "deny",
"tools": {
"add-contact-to-segment": {
"limits": [
{
"counter": "add-contact-to-segment_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add-contact-to-segment 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.
Add a contact to a segment in Resend (by contact ID or email). It is categorised as a Write tool in the Email Sending MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Email Sending MCP server in PolicyLayer and add a rule for add-contact-to-segment: 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 Email Sending MCP. Nothing to install.
add-contact-to-segment 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 add-contact-to-segment 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 add-contact-to-segment. 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.
add-contact-to-segment is provided by the Email Sending MCP server (resend/resend-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 77 Email Sending MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
77 Email Sending MCP tools catalogued and risk-classified — across an index of 42,500+ MCP servers.