Email Deliverability: Why Your Emails Land in Spam

I've seen businesses spend thousands on email marketing tools and then wonder why their open rates are 5%. The tool isn't the problem. The domain authentication is. Gmail and Outlook now reject or filter email from domains that aren't properly configured with SPF, DKIM, and DMARC.

SPF: Tell Receiving Servers Who Can Send For You

SPF (Sender Policy Framework) is a DNS TXT record that lists the mail servers authorised to send email from your domain. Your email service will give you an SPF record to add:

v=spf1 include:mailgun.org ~all

Use -all (hard fail) once you're confident you've listed every sending source.

DKIM: Cryptographic Proof the Email Wasn't Tampered With

DKIM adds a digital signature to outgoing emails, verified against a public key in your DNS. Your email provider generates the key pair. You add the public key to DNS as a TXT record. Receiving servers verify the signature — if it matches, the email came from you and wasn't altered in transit.

DMARC: Tell Receiving Servers What to Do With Failures

Start with a monitoring-only policy:

v=DMARC1; p=none; rua=mailto:[email protected]

Review aggregate reports for two weeks, then move to p=quarantine and eventually p=reject.

The Content Side of Deliverability

Authentication gets you in the door. Content keeps you there. Send to people who actually signed up, segment your list so emails are relevant, and make the unsubscribe link easy to find.