AI agents call get_header_field to retrieve information from Imap without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool only reads (retrieves) an email message header field value for a specified message UID. It performs no write, delete, execute, or financial operations. The action is purely informational and cannot cause data loss or harmful side effects.
From the tool's definition Tool name is 'get_header_field' and description states 'Read a message header field' — retrieves metadata without modification or side effects.
Attacks that exploit this kind of access
Read a message header field for the given uid in directory. It is categorised as a Read tool in the Imap MCP Server, which means it retrieves data without modifying state.
Register the Imap MCP server in PolicyLayer and add a rule for get_header_field: 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 Imap. Nothing to install.
get_header_field is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the get_header_field 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 get_header_field. 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.
get_header_field is provided by the Imap MCP server (vivier/imap-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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