Fix guide
How to Fix DMARC Alignment for Fastmail
Fastmail DMARC alignment works automatically when you host your domain with Fastmail's DNS. For external DNS providers, add Fastmail's SPF include and DKIM TXT record.
Why alignment fails
External DNS without Fastmail's SPF and DKIM records breaks alignment for outbound mail.
Exact DNS records
SPF: include:spf.messagingengine.com
DKIM: TXT at fm1._domainkey / fm2._domainkey / fm3._domainkey (per Fastmail UI)
Step-by-step fix
Step 1 Fastmail → Settings → Domains
Step 2 Copy SPF include:spf.messagingengine.com and DKIM TXT
Step 3 Add DKIM at fm1._domainkey / fm2 / fm3 as Fastmail shows
Step 4 Ensure single SPF TXT with include:spf.messagingengine.com
Step 5 Wait for DNS propagation
Step 6 Confirm DKIM and alignment with DNS Preflight
Verify alignment and DNS in your browser
Open DNS Preflight →FAQ
Fastmail DNS vs external DNS for DMARC?
Fastmail can manage DNS for you with one click. On external DNS, manually add SPF and DKIM TXT values from Fastmail settings.
What DKIM selectors does Fastmail use?
Fastmail may use fm1, fm2, fm3 selectors — follow the exact hostnames in your domain panel.
What SPF include does Fastmail need?
include:spf.messagingengine.com in your SPF TXT.
How do I verify Fastmail DKIM?
Fastmail shows status when records are correct. DNS Preflight can verify public DKIM keys.
Does Fastmail support DMARC p=reject?
Yes when alignment passes — monitor reports.