SPF (Sender Policy Framework, RFC 7208) authorizes specific servers to send mail for your domain. When you start sending through Fastmail, you must publish a single SPF record at your domain apex that includes Fastmail's sending infrastructure — otherwise the messages will fail SPF, your DMARC checks will fail, and your mail will land in spam or be rejected outright.
If you already publish SPF for another sender (Google Workspace for inbound, a marketing tool, your CRM), do not publish a second record. Merge the new include into the existing record. RFC 7208 §3 forbids multiple SPF records on the same name and receivers MUST return permerror when they see one.
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.
- Type
TXT- Host
@- Value
v=spf1 include:spf.messagingengine.com ?all
- Fastmail recommends `?all` (neutral) on apex SPF for domains that send through multiple providers. Use `~all` or `-all` if Fastmail is your only sender.
Where in Fastmail
The SPF configuration lives in Fastmail → Settings → Domains → <your-domain> → Authentication.
Verify the records
Once published, run the SPF Checker on your domain to verify the lookup chain expands cleanly and stays under the 10-DNS-lookup limit.
dig +short TXT your-domain.comCommon pitfalls
- 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.