SPF, DKIM and DMARC are DNS records that prove email from your domain is really yours: SPF lists who may send for it, DKIM signs each message, and DMARC tells inboxes what to do when those checks fail.
How it works
All three are records you publish in your domain's DNS. Receiving servers look them up for every message that claims to come from your domain.
- SPF (Sender Policy Framework) lists the servers allowed to send mail for your domain. Mail from a server that isn't listed can be rejected.
- DKIM (DomainKeys Identified Mail) adds a signature to each message. Your sending provider signs with a private key, and the public key sits in your DNS. Gmail requires a key of at least 1024 bits.
- DMARC sets a policy for mail that fails. A message passes DMARC when SPF or DKIM passes and the authenticated domain matches the domain in the From header. That match is called alignment.
A starting DMARC record looks like this. p=none only monitors, and rua names where reports go:
v=DMARC1; p=none; rua=mailto:dmarc-reports@example.com
Why it matters
- Gmail requires it. Every sender needs SPF or DKIM. Anyone sending 5,000 or more messages a day to Gmail needs SPF, DKIM and DMARC. Unauthenticated mail may be marked as spam or rejected.
- Yahoo requires it too. Bulk senders need SPF and DKIM, and a DMARC policy of at least
p=nonethat passes. - It exposes impersonation. Without these records, receiving servers can't tell your mail from mail that only pretends to come from your domain.
How Mimeo handles it
You set these records up for your sending domain at your provider and your DNS host, not in Mimeo. When you verify a domain, Postmark or Resend shows the DNS records to add (Set up sending). DMARC is one more record you publish at your DNS host.
Mimeo reads back which domains and senders your provider has verified, and checks each email's From address against that list before it sends. Mail from a domain that isn't verified yet holds in the queue with the reason shown, and goes out by itself once the domain turns green (Sending domains & senders). Separately, one CNAME connects the domain to Mimeo, so tracking and unsubscribe links ride your own domain and match the From address. See Mimeo terms for DKIM and SPF in Mimeo's own words.
- Email sender guidelines. Checked .
- Sender best practices. Checked .
- Sending domains & senders. Checked .
- Postmark setup. Checked .
- Resend setup. Checked .