Update an existing topic in Resend. Note: defaultSubscription cannot be modified after creation.
AI agents use update-topic 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 modifies existing email topic settings in Resend, which is a reversible write operation. It does not delete data (ruling out Destructive), does not execute arbitrary code or external commands (ruling out Execute), does not move money (ruling out Financial), and performs more than a simple read.
From the tool's definition Tool name 'update-topic' and description 'Update an existing topic in Resend' indicates modification of data. The note about 'defaultSubscription cannot be modified after creation' confirms the tool performs reversible updates to topic configuration.
Documented attack patterns abuse exactly the kind of access update-topic 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-topic:
{
"version": "1",
"default": "deny",
"tools": {
"update-topic": {
"limits": [
{
"counter": "update-topic_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}update-topic 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.
Update an existing topic in Resend. Note: defaultSubscription cannot be modified after creation. 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-topic: 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-topic 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-topic 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-topic. 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-topic 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.