Email & DNS

DMARC Record Builder

Build a current DMARC TXT policy for a domain.

Calculations run in your browser. The tool does not send your inputs to a server.

01Your inputs

Local workspace

Start with the sample below, or enter your own values.

Domain

Domain policy

Subdomain policy

Policy application

DKIM alignment

SPF alignment

Optional aggregate report addressUse a complete reporting URI such as mailto:dmarc-reports@example.com. External destinations may require DNS authorisation.

Optional failure report addressUse a complete reporting URI such as mailto:dmarc-reports@example.com. External destinations may require DNS authorisation.

02Your result

Your result will appear here. Choose an action after checking your inputs.

A quick guide

How to use this tool

Check the example and the unit beside each input.
Enter your values and choose Build.
Review the result and assumptions, then copy what you need.

Reset example restores the starting values. Clear removes text and number inputs, returns choices to their first valid option, and removes the result.

Reference guide

Explanation and worked examples

DMARC compares the visible From domain with validated SPF or DKIM identifiers. RFC 9989 uses t=y for testing a stricter policy one level lower; the older pct rollout tag is obsolete.

Use in day-to-day IT work

Prepare a mail or DNS change, or interpret evidence from a delivery investigation.

Checks before applying the result

Record existing DNS values and TTLs, identify the authoritative provider, and prepare rollback values.
After publishing, query authoritative DNS and check actual message headers or delivery reports. These tools do not query live services.

New to the terminology?

SPF: Sender Policy Framework: authorises sending hosts for a domain used by SMTP.
MTA-STS: A published policy for authenticated TLS delivery to declared MX hosts.
TTL: How long a DNS answer may normally remain cached.

Keep exploring

How calculations work and where the models stop →