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Email authentication is a set of protocols that verify the sender identity of an email message. The three main authentication methods are SPF, DKIM, and DMARC, which work together to prove that emails actually come from your domain and have not been tampered with during transit.
Email authentication directly impacts your deliverability and brand protection. Without proper authentication, email providers like Gmail and Outlook are more likely to mark your messages as spam or reject them entirely. Major email providers now require authentication for bulk senders - Google and Yahoo mandated SPF, DKIM, and DMARC for senders of 5,000+ daily emails starting February 2024. Authentication also prevents bad actors from spoofing your domain to send phishing emails that damage your brand reputation.
Email authentication uses DNS records to verify sender identity. SPF (Sender Policy Framework) specifies which mail servers can send emails on behalf of your domain. DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each email that receiving servers can verify against a public key in your DNS. DMARC (Domain-based Message Authentication, Reporting and Conformance) ties SPF and DKIM together and tells receiving servers what to do when authentication fails - quarantine the message, reject it, or allow it through. When all three protocols align, receiving servers can trust that your emails are legitimate.
Yes, implementing all three provides the strongest protection. SPF and DKIM verify different aspects of email authenticity, while DMARC provides policy enforcement and reporting. Major email providers like Gmail now require all three for bulk senders.
When authentication fails, receiving servers may reject your email, send it to spam, or accept it with warnings depending on your DMARC policy and the receiving server's configuration. Authentication failures hurt your sender reputation over time.
DNS only allows one SPF record per domain. If you have multiple services sending email, combine all authorized senders into a single SPF record using include statements. For example: v=spf1 include:_spf.google.com include:sendgrid.net -all
DNS changes typically propagate within 24-48 hours, though many servers update faster. Use low TTL values when making changes so updates propagate quickly. Always test your authentication before sending large campaigns.
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