Email & DNS

DMARC Alignment Checker

Check strict or relaxed DMARC identifier alignment from supplied domains.

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.

RFC5322.From domain

Organisational domainEnter the organisational domain determined by DMARC DNS tree-walk rules, such as example.com for news.example.com.

SPF-authenticated MAIL FROM domain

DKIM signing domain (d=)

SPF alignment

DKIM alignment

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 Check.
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

Strict alignment requires an exact domain match. Relaxed alignment requires the same organisational domain; this offline check relies on the organisational domain you provide.

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 →