AI agents use update-contact 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.
The tool creates or modifies data reversibly by updating contact records. While it affects data, updates are generally reversible (contact information can be corrected or reverted), distinguishing it from destructive deletion. Severity is medium because misuse could modify user contact data at scale, affecting email operations and user privacy, but the changes are not irreversible.
From the tool's definition Tool description states 'Update a contact in Resend (by ID or email)' — directly modifies existing contact data via API. This is a reversible write operation that changes contact properties.
Documented attack patterns abuse exactly the kind of access update-contact 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 update-contact:
{
"version": "1",
"default": "deny",
"tools": {
"update-contact": {
"limits": [
{
"counter": "update-contact_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update-contact 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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Update a contact in Resend (by 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 update-contact: 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.
update-contact 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 update-contact 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 update-contact. 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.
update-contact 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.