Why Your Emails Go to Spam: SPF, DKIM, and DMARC Explained

When email goes to spam, the content is usually not the main cause. Mailbox providers such as Gmail, Outlook, and Yahoo look first at who is sending the message and how that sender has behaved in the past. Three things carry most of the weight: authentication, reputation, and engagement.

Authentication: proving the mail is yours

Anyone can put your domain in the From line of an email. Authentication is how a receiving server checks that a message claiming to be from you actually is. It relies on three records published in your domain's DNS.

SPF

SPF, or Sender Policy Framework, is a list of the servers that are allowed to send email for your domain. When a message arrives, the receiving server checks whether it came from a server on that list. If you send through an email platform, that platform has to be included in your SPF record.

DKIM

DKIM, or DomainKeys Identified Mail, adds a digital signature to each message. The receiving server uses a public key in your DNS to confirm the signature, which shows the message was authorized by your domain and was not altered on the way.

DMARC

DMARC ties the other two together. It tells receiving servers what to do with a message that fails SPF and DKIM checks: deliver it anyway, send it to spam, or reject it. It also sends you reports showing who is sending mail in your domain's name. Most senders start with a monitoring-only policy, read the reports, fix what is failing, and then tighten the policy.

What Gmail and Yahoo require

Since February 2024, Gmail and Yahoo have enforced requirements for bulk senders, which Google defines as those sending around 5,000 or more messages a day to Gmail addresses. In summary:

• Authenticate with both SPF and DKIM, and publish a DMARC record.
• Offer one-click unsubscribe in marketing messages and honor requests promptly.
• Keep the spam complaint rate low. Google's guidance is to stay below 0.1% and never reach 0.3%.

Senders that fall short see their mail delayed, sent to spam, or rejected.

Reputation: your sending history

Every sending domain and IP address builds a reputation over time. Bounces, spam complaints, and hits on spam traps lower it. Consistent volume and positive engagement raise it. A new domain has no reputation at all, which is why sending volume has to be increased gradually, a process known as warming up.

Engagement: how recipients react

Providers watch what people do with your mail. Opens, clicks, and replies are good signs. Deleting without reading and marking as spam are bad ones. Sending to people who never engage teaches providers to filter your mail for everyone.

The other common causes

• An unclean list. Old addresses produce bounces and spam trap hits. See our guide on how to clean an email list.
• Sudden spikes in volume. A quiet domain that abruptly sends a large campaign looks like a compromised account.
• Blocklists. If your domain or IP is on a major blocklist, many providers will refuse your mail until it is removed.
• No easy way to unsubscribe. People who cannot find the unsubscribe link use the spam button instead.

A short checklist

• Confirm SPF, DKIM, and DMARC are all set up and passing.
• Set up Google Postmaster Tools to see your domain's reputation and spam rate.
• Check whether your domain or IP is on any blocklists.
• Validate your list and remove inactive contacts.
• Increase volume gradually after any long pause.

When to get help

If you have fixed authentication and cleaned your list and mail is still landing in spam, the reputation of the domain itself usually needs rebuilding. R1D Media Group's email deliverability service covers authentication, blocklist removal, and reputation warmup, and our data validation removes the addresses that cause the damage in the first place.