AI agents use sendHtmlMail to create or update resources in Mail MCP Tool — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Mail MCP Tool environment.
Sending emails is a Write operation—it creates new data (outbound messages) with reversible side effects. Severity is high because misconfigured email sending could spam users, send sensitive information to wrong recipients, or be weaponized for phishing/social engineering at scale. An AI agent with this capability could cause reputational harm, data leaks, or compliance violations (CAN-SPAM, GDPR).
From the tool's definition Tool name 'sendHtmlMail' indicates sending emails with HTML content. Server description confirms this tool enables 'sending emails' as part of email operations.
Documented attack patterns abuse exactly the kind of access sendHtmlMail gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Mail MCP Tool, and nothing reaches the server without passing your rules. This is the rule we recommend for sendHtmlMail:
{
"version": "1",
"default": "deny",
"tools": {
"sendHtmlMail": {
"limits": [
{
"counter": "sendhtmlmail_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}sendHtmlMail 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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sendHtmlMail. It is categorised as a Write tool in the Mail MCP Tool MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Mail MCP Tool MCP server in PolicyLayer and add a rule for sendHtmlMail: 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 Mail MCP Tool. Nothing to install.
sendHtmlMail 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 sendHtmlMail 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 sendHtmlMail. 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.
sendHtmlMail is provided by the Mail MCP Tool MCP server (shuakami/mcp-mail). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 17 Mail MCP Tool tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
Free to start. No card required.
17 Mail MCP Tool tools catalogued and risk-classified — across an index of 42,500+ MCP servers.