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    Chapter · DMARC for Fastmail
    Revised 17 Jun 2026
    Guide · DMARC · Fastmail

    How to set up DMARC for Fastmail.

    Fastmail is a privacy-oriented business mail provider. Their DKIM CNAMEs are the cleanest of any major ESP — three records, fixed names, point at hosted keys.

    Afsan Rahmatullah
    Afsan RahmatullahMailerMonk

    DMARC (RFC 7489) tells receiving mail servers what to do when a message claiming to be from your domain fails SPF or DKIM. You publish exactly one DMARC record at `_dmarc.<your-domain>`, regardless of which ESP you use — DMARC is a domain-level policy, not a per-sender configuration. Fastmail doesn't run DMARC for you, but their SPF + DKIM setup is what makes your DMARC checks pass.

    Start every domain at `p=none` with a `rua` (aggregate report) address pointing somewhere you actually read. Watch the reports for two to four weeks to confirm 100% of legitimate mail is aligned, then progress to `p=quarantine` and finally `p=reject`. Skipping the monitoring step is the single most common way founders accidentally block their own mail.

    Publish these DNS records

    Add the following record(s) to your domain's DNS zone. Most registrars (Cloudflare, Route 53, Namecheap, GoDaddy) accept values exactly as shown.

    Record · TXT
    Type
    TXT
    Host
    _dmarc
    Value
    v=DMARC1; p=none; rua=mailto:dmarc-reports@your-domain.com

    Where in Fastmail

    The DMARC configuration lives in Fastmail → Settings → Domains → <your-domain> → Authentication.

    Verify the records

    Once published, run the DMARC Checker on your apex domain to confirm the record parses, reporting URIs are valid, and the policy is what you intended.

    From a terminal
    dig +short TXT _dmarc.your-domain.com
    Run the free DMARC checker

    Common pitfalls

    Pitfall
    • Fastmail expects you to publish their MX records as well; without MX pointing at `in1-smtp.messagingengine.com` and `in2-smtp.messagingengine.com`, inbound mail won't reach the mailbox even if SPF/DKIM/DMARC are fine.
    • Fastmail's masked-email feature uses a different sending IP pool. Outbound from masked addresses still aligns with your domain DKIM if you've configured custom domain sending.
    After you publish

    Want to know if it actually keeps working?

    MailerMonk continuously watches your DMARC record, aggregate DMARC reports, and inbox placement — and pings you the moment something drifts. Free for the first domain.

    Start free trial

    About the author

    Afsan Rahmatullah
    Afsan Rahmatullah
    MailerMonk

    Building tools that keep cold email out of spam. Writes about deliverability, DMARC, and what actually moves inbox placement.

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