How to Set Up DKIM for Fastmail

Enable DKIM for Fastmail by publishing three CNAME records for the fm1, fm2, and fm3 selectors.

Quick Answer — The Record You Need

Record Type

CNAME

Host / Name

fm1._domainkey

Value

fm1.yourdomain.com.dkim.fmhosted.com

Fastmail uses three DKIM selectors: fm1, fm2, and fm3. All three CNAME records must be added.

Step-by-Step Setup

Log in to Fastmail

Go to fastmail.com and sign in.

Navigate to domain settings

Go to Settings > Domains. Select your custom domain.

View the DKIM records

Fastmail displays three CNAME records for DKIM with selectors fm1, fm2, and fm3.

Add all three CNAME records

Create the three CNAME records in your DNS provider.

fm1._domainkey.yourdomain.com  CNAME  fm1.yourdomain.com.dkim.fmhosted.com
fm2._domainkey.yourdomain.com  CNAME  fm2.yourdomain.com.dkim.fmhosted.com
fm3._domainkey.yourdomain.com  CNAME  fm3.yourdomain.com.dkim.fmhosted.com

Verify in Fastmail

Fastmail will verify the DKIM records and activate signing.

Common Gotchas

Fastmail requires all three CNAME records (fm1, fm2, fm3). This allows key rotation without downtime.
The CNAME values include your domain name in the target: fm1.yourdomain.com.dkim.fmhosted.com. Replace yourdomain.com with your actual domain.
If you manage DNS through Fastmail directly (using their nameservers), DKIM is configured automatically.

Verify Your Setup

After adding your DNS records, use our free DKIM checker to verify everything is configured correctly. DNS changes typically propagate within minutes, but can take up to 48 hours.

Frequently Asked Questions

What DKIM selectors does Fastmail use?

Fastmail uses fm1, fm2, and fm3 as DKIM selectors. All three are published as CNAME records pointing to fmhosted.com.

Why does Fastmail use three DKIM selectors?

Three selectors allow Fastmail to rotate DKIM keys smoothly. One selector is active while others are prepared for rotation.

Can Fastmail manage my DNS and DKIM automatically?

Yes. If you use Fastmail's nameservers for your domain, DKIM (and all other records) are configured automatically.