Fastmail receives mail for 24 of 9,971 popular domains we measured in November 2026. Below: the records it needs and how its customers actually set them.
| Host | Priority |
|---|---|
in1-smtp.messagingengine.com | 10 |
in2-smtp.messagingengine.com | 20 |
Add include:spf.messagingengine.com to the domain's single SPF record, for example:
v=spf1 include:spf.messagingengine.com -all23 of 24 Fastmail customers in our sample (95.8%) have this include in their SPF record.
Three CNAME records, fm1._domainkey, fm2._domainkey and fm3._domainkey, pointing to fm1.<domain>.dkim.fmhosted.com (and fm2/fm3).
Publish a TXT record at _dmarc.<domain> once SPF and DKIM pass for all mail you send, start with p=none and a reporting address, then move to p=quarantine or p=reject:
v=DMARC1; p=reject; rua=mailto:dmarc-reports@<domain>Official documentation: MX
Provider site: https://www.fastmail.com/
24 customer domains in the sample (accent bars) compared with all 9,971 measured domains (grey bars).
The highest-ranked domains in the sample whose MX records point to Fastmail.
Check one yourself:
Customer-specific parts replaced by <domain> and digits by <n>.
| MX host pattern | Domains |
|---|---|
in<n>-smtp.messagingengine.com | 24 |
Source: our own scan of November 2026 (2026-11-11), 9,971 of the top 10,000 domains of the Tranco list Y895G that answered in DNS. Method and data.