Email Authentication Tools

Validate SPF, DKIM, DMARC, and PTR records to ensure your emails are authenticated and trusted by receiving servers.

SPF (Sender Policy Framework)

SPF records specify which mail servers are authorized to send email on behalf of your domain. Proper SPF configuration prevents email spoofing and improves deliverability.

Key Features

  • Validate SPF record syntax and structure
  • Check for the critical 10-DNS-lookup limit
  • Identify authorized sending servers and IP addresses
  • Detect common misconfigurations and errors
  • Verify SPF mechanisms (ip4, ip6, include, a, mx)

Why It Matters

Email providers like Gmail, Outlook, and Yahoo require SPF authentication. Without it, your emails may be rejected or marked as spam. The 10-DNS-lookup limit is especially critical - exceeding it causes SPF validation to fail completely.

DKIM (DomainKeys Identified Mail)

DKIM uses cryptographic signatures to verify that emails haven't been tampered with in transit. It proves the email actually came from your domain.

Key Features

  • Validate DKIM signatures and public keys
  • Check key length (1024-bit vs 2048-bit recommended)
  • Verify selector configuration
  • Test signature alignment with your domain
  • Identify expired or invalid keys

Best Practices

Use 2048-bit keys for better security. Rotate keys annually. Sign all outgoing mail with DKIM, not just marketing emails. Gmail and Yahoo now require DKIM for bulk senders (5,000+ emails/day).

DMARC (Domain-based Message Authentication)

DMARC builds on SPF and DKIM to tell receiving servers what to do when authentication fails. It protects your domain from spoofing and phishing attacks.

Key Features

  • Analyze DMARC policy (none, quarantine, reject)
  • Check alignment modes (strict vs relaxed)
  • Validate reporting addresses (rua, ruf)
  • Verify subdomain policy configuration
  • Test percentage-based rollout (pct tag)

Policy Recommendations

Start with p=none to monitor authentication failures without blocking mail. Gradually move to p=quarantine, then p=reject as you fix issues. Set up aggregate reports (rua) to track authentication results across all your sending sources.

PTR Records (Reverse DNS)

PTR records provide reverse DNS lookup, mapping IP addresses back to domain names. They're essential for email server reputation and deliverability.

Key Features

  • Verify reverse DNS (PTR) configuration
  • Check forward-confirmed reverse DNS (FCrDNS)
  • Test IP-to-hostname mapping
  • Identify mismatched or missing PTR records
  • Validate against sending IP addresses

Why Configure PTR Records

Many email servers reject mail from IPs without valid PTR records. FCrDNS (forward-confirmed reverse DNS) ensures your IP's PTR record matches a forward DNS lookup. This improves sender reputation and reduces spam filtering.

Complete Authentication Setup Guide

Step 1: Configure SPF

Create an SPF record listing all authorized mail servers. Keep it under 10 DNS lookups. Use the SPF checker to validate.

Step 2: Enable DKIM

Generate a 2048-bit DKIM key pair. Add the public key to DNS with your selector. Configure your mail server to sign all outgoing messages.

Step 3: Implement DMARC

Start with p=none and set up aggregate reporting. Monitor for 2-4 weeks, fix any authentication issues, then move to p=quarantine or p=reject.

Step 4: Verify PTR Records

Work with your hosting provider or ISP to set up PTR records for all sending IPs. Ensure FCrDNS matches your mail server's hostname.