How to set up DKIM on Fastmail

Step by step DKIM setup for Fastmail: complete instructions, examples, verification commands, and common pitfalls.

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This is a reference guide for configuring DKIM on Fastmail. Use it while editing DNS or when troubleshooting deliverability.

Tip: Avoid common mistakes: follow these steps to add DKIM on Fastmail. Then verify everything with the InboxGreen Free Checker.

Provider-specific notes for Fastmail

  • Different dashboards label DNS fields differently. Always verify the published record using dig or a checker.
  • If records look right but still fail, it is usually caching, propagation delay, or a host name mismatch.
  • Fastmail Settings → Domains → DNS Configuration.

What you’ll need

  • Access to Fastmail to generate a DKIM key and selector.
  • DNS provider access to publish a TXT record at selector._domainkey.

Generate your DKIM key

In Fastmail, generate a DKIM key and note the selector. Providers often suggest something like fm1 and fm2.

Fastmail Settings → Domains → DNS Configuration.

Publish the record

  1. Create a TXT record at host selector._domainkey (replace selector with your actual selector name).
  2. Paste the full value starting with v=DKIM1; k=rsa; p= and save.
  3. Wait for DNS propagation.

Verify DKIM

  • Send a test email to a Gmail address and use “Show original” to confirm “DKIM: PASS”.
  • Or run: 
    dig TXT selector._domainkey.yourdomain.com +short

Common mistakes

  • Using the wrong host so the record becomes selector._domainkey.yourdomain.com.yourdomain.com.
  • Breaking the value by wrapping or truncating the TXT string.
  • Publishing a record for the wrong selector and then validating on another.

Related for Fastmail

quick_reference_all Set up SPF on Fastmail quick_reference_all Set up DMARC on Fastmail quick_reference_all Set up List-Unsubscribe on Fastmail
Pro tip: Turn on InboxGreen Monitoring to check these records daily and get alerts if something breaks.

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