Build a DMARC policy record
Tune policy, alignment and report destinations for the _dmarc TXT record. All assembly runs locally in your browser.
v=DMARC1; p=none; rua=mailto:dmarc-reports@example.com; adkim=r; aspf=r; fo=1
How to roll out DMARC
Start with monitoring, watch the aggregate reports, then ramp policy strength. Never skip the rua address.
- 01
Start at p=none
Receivers report failures but still deliver — gives you visibility without breaking mail.
Lookups reference the IANA registries (MIME, HTTP status, TLDs) bundled at build time — no live network calls, no rate limits, no leaked queries.
monitorIANAregistryofflinelivepolicy · querynone · IANAp=none
loaded · IANA bundlespec · ready - 02
Add rua reports
Point rua to a mailbox or DMARC service that aggregates failures.
Builders emit canonical syntax per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs) so the output passes spec-compliant parsers.
reportsRFC 9110canonicalspec-compliantliverua · optionsset · liverua=mailto:reports@…
options applied · livecanonical - 03
Ramp pct + policy
Move pct from 10 to 100 over weeks, then upgrade p to quarantine then reject.
Validation flags common pitfalls — uppercase header names, smart quotes inside
Content-Type, missing;charset=utf-8— before they bite production.rolloutvalidationlintpitfallslivepct · looked up100 · readyp=quarantine; pct=50
result · livevalidated - 04
Tighten alignment
Switch adkim/aspf to s once subdomains and ESPs all align correctly.
Copy writes the snippet directly into your clipboard; downloads emit the right extension and MIME so curl/httpie pick them up correctly.
enforceclipboardMIME-correctblobcurl-readyok · copiedstrict · donep=reject; adkim=s; aspf=s
shipped · ready to shipsuccess
Web-spec details that bite later
Idempotency saves retries
POST/PUT/DELETE should be safely retried. Use idempotency keys and return the same response on duplicate requests.
Match RFC 9110 status codes
Don’t invent codes. 422 for validation errors, 409 for conflicts, 429 for rate limits. Standard codes work with off-the-shelf clients.
Set <code>Cache-Control</code> deliberately
Default browser caching is conservative. Use max-age + stale-while-revalidate for hot endpoints.
Validate Open Graph in dev
OG tags break silently. Use a previewer like OG Generator + Facebook’s debugger before launch.
CORS is a server concern
The browser sends the preflight; the server decides. Wildcard origins disable credentials — be explicit.
MIME drives behaviour
Servers must send the right Content-Type. Browsers sniff but the spec says they shouldn’t — be explicit to avoid surprises.
When to publish DMARC
Sender reputation, anti-phishing, audit trails.
Anti-phishing
Reject mail forging your envelope-from. Bundled from IANA registries at build time — no live network call, no rate limit, no leaked queries. The MIME, TLD, and status-code tables are baked in so the tool works offline once loaded.
spec-compliantBIMI prep
Brand logos in Gmail require DMARC at quarantine+. Output is canonical per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs), so spec-compliant parsers accept it as-is. Cross-browser and cross-library behaviour stays consistent.
offlineCompliance
Some regulators (HHS, FTC) require DMARC reject. Pairs with the curl-to-fetch converter for end-to-end test stubs — copy the curl from DevTools, paste, get an idiomatic fetch() body. Drop into Playwright/Vitest fixtures without manual translation.
IANA-backedAggregate reports
Spot unauthorized senders in your domain. Catches common pitfalls (uppercase header names, smart quotes inside Content-Type, missing ;charset=utf-8) before they bite production. Validation flags rather than auto-corrects so you stay in control.
RFC-alignedRollout safety
pct lets you ramp policy without breaking everything. Validation runs as you type — copy only when the output is shaped correctly. The output drops directly into nginx, Apache, or CDN configs without re-formatting or re-quoting.
production-gradeSubdomain control
Lock down subdomains tighter than the parent. Same input plus same options always produces identical canonical output, so the tool is safe to embed in CI scripts that diff against expected configs.
curl-readyFrequently asked questions
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