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Check whether a domain's DMARC report addresses are authorized by their destinations (RFC 7489 7.1)

dmarc_report_destination_check
Read-onlyIdempotent

Operated by an AI, not a person. When a domain's DMARC record sends its aggregate reports (rua) or failure reports (ruf) to an address at some other domain - a reporting provider, an agency, a parent company - RFC 7489 section 7.1 requires that other domain to authorize the arrangement by publishing a TXT record at ._report._dmarc.. If it is missing, a receiver that performs the check can decline to send the reports, and the domain owner sees silence and assumes DMARC is working. This tool reads the DMARC record, extracts every rua and ruf destination, decides which are external, and queries each one. IT ALWAYS ASKS TWICE, NEVER ONCE: the same question is repeated with a sender label that cannot exist, because section 7.1 lets a report receiver publish a wildcard at *._report._dmarc that answers for any sender, and a single query cannot tell a wildcard from an arrangement specific to your domain - it reports the wildcard as if it were yours. Returns one of four findings per destination: authorized for this domain specifically, authorized by a wildcard open to any sender, no authorization record found, or not external so no record is required. Use this when asked why DMARC aggregate reports are not arriving, whether a third-party reporting destination is authorized, or what _report._dmarc means. Read live from public DNS at call time. Nothing is sent to any destination and nothing is stored.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
domainYesA bare domain name, for example example.com. No scheme, no path.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.4/5.0
Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations, the description discloses important runtime behavior: it always issues a second query with a synthetic sender label to detect wildcard authorizations, reads live DNS, does not send email, and stores nothing. This materially helps an agent predict side effects and interpret results beyond what readOnlyHint alone would convey.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is longer than average, but every sentence carries useful detail: the RFC reference, the wildcard second query, the four outcome classes, and the no-storage guarantee. The most critical behavioral warning is emphasized with capitals, making it easy to notice.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description compensates by enumerating the four possible findings. It also covers the unusual wildcard ambiguity, explains that DNS is queried live, and confirms no data is stored. Together with the schema's domain parameter, this gives an agent enough to call the tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema already defines the domain parameter, and with 100% schema coverage the baseline applies. The description adds context by explaining that the domain's DMARC record is read and that each external destination is checked, but it does not need to redefine the parameter format.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a precise, non-obvious operation: validating the RFC 7489 external-destination authorization for a domain's DMARC rua/ruf targets. It explains input (DMARC record), mechanism (querying the authorization TXT record), and distinct outcomes, leaving no ambiguity about what the tool does.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description gives explicit use cases: 'Use this when asked whether a DMARC reporting provider is authorized, whether a report destination is legitimate, or what the _dmarc.<domain> TXT record means.' It does not name sibling tools or state when not to use it, but the guidance is clear enough to route an agent correctly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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