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mx · dns · bind zone · email

Format MX records with priorities

Build BIND-style MX records for mail server failover. Lower priority numbers are tried first.

MX Record Builder
Domain
example.com
host
Records
2
mx
Primary
10
lowest
Failover
yes
redundancy
Domain
input · mx servers

Lower priority numbers are preferred. Use multiple servers with different priorities for failover.

output · bind zone
example.com.    IN    MX    10    mail1.example.com.
example.com.    IN    MX    20    mail2.example.com.
Quick Start

How MX records work

Sending mail servers query MX records to find where to deliver mail for your domain. Multiple records with different priorities give failover.

  1. 01

    List mail hosts

    Add the fully-qualified hostname of each mail server.

    Lookups reference the IANA registries (MIME, HTTP status, TLDs) bundled at build time — no live network calls, no rate limits, no leaked queries.

    hostsIANAregistryofflinelive
    hosts · querymx · IANA
    mail1.example.com
    loaded · IANA bundlespec · ready
  2. 02

    Assign priorities

    Lower wins. Use 10, 20, 30 spacing to leave room.

    Builders emit canonical syntax per the relevant RFC (9110 for HTTP, 5322 for headers, 3986 for URLs) so the output passes spec-compliant parsers.

    priorityRFC 9110canonicalspec-compliantlive
    priority · options10/20 · live
    10 mail1 · 20 mail2
    options applied · livecanonical
  3. 03

    Publish records

    Add each as an MX record at your DNS provider for the apex.

    Validation flags common pitfalls — uppercase header names, smart quotes inside Content-Type, missing ;charset=utf-8 — before they bite production.

    dnsvalidationlintpitfallslive
    dns · looked upmx · ready
    @ MX 10 mail1...
    result · livevalidated
  4. 04

    Verify

    Run dig +short MX example.com to confirm propagation.

    Copy writes the snippet directly into your clipboard; downloads emit the right extension and MIME so curl/httpie pick them up correctly.

    verifyclipboardMIME-correctblobcurl-ready
    ok · copiedready · done
    dig MX example.com
    shipped · ready to shipsuccess
Pro tips

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.

Related toolsSPF RecordDKIM RecordDMARC RecordDNS LookupDNSSECReverse DNS
Use Cases

When to format MX records

Email setup, failover, vendor migration.

New domain email

Point a fresh domain to Google Workspace or Microsoft 365. 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-compliant

Failover

Two MX hosts so mail keeps flowing if one is down. 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.

offline

Migrating ESP

Shift mail to a new provider with priority weighting. 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-backed

Subdomain mail

Set separate MX for noreply.example.com or txn.example.com. 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-aligned

Outsourced inbound

Run anti-spam at the edge via a third-party MX. 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-grade

Geo distribution

Multiple MX hosts in different regions. 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-ready
FAQ

Frequently asked questions

Sending servers try the lowest-priority MX first; if that fails they fall back to the next. Equal priorities are tried in round-robin order.
No — MX targets must be A/AAAA records, not CNAMEs. Most DNS providers warn you if you try.
Fully-qualified domain names in BIND zone files end with a dot. Most DNS UIs add it for you.
TTL-bound — usually minutes to hours. New domains may need a full day for the worst caches.
Yes. Generation is entirely client-side.
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