How Email Authentication Works

These are the main methods that help verify emails are genuine:

Sender Verification (SPF)

🔒 What SPF Does:

• Creates a list of approved email servers for a domain
• Prevents others from pretending to send from that domain
• Works like a VIP guest list for your email

🛡️ How It Protects You:

1. When you get an email, your provider checks:
   • Is the sending server on the domain's approved list?
   • If not, the email might be fake

📋 Common SPF Results:

• ✅ Pass: Server is authorized (good)
• ❌ Fail: Server isn't authorized (likely fake)
• ⚠️ Softfail: Suspicious but not definitely fake
• ➖ Neutral: Domain hasn't set SPF rules
• ❓ None: No SPF record exists

🌟 Real World Example:

A bank's SPF record might include:

• Their mail servers
• Marketing email providers
• Fraud detection services

💡 Tip: Legitimate businesses always have SPF records. Missing SPF is a red flag.

⚠️ Limitation: SPF alone can't prevent all spoofing - it works best with DKIM and DMARC.

Email Signatures (DKIM)

🔏 What DKIM Does:

• Adds a digital "fingerprint" to each email
• Proves the message wasn't changed in transit
• Works like a tamper-proof seal on documents

🛡️ How It Protects You:

1. Sender creates signature using private key
2. Your email provider verifies using public key
3. Three possible results:
   • ✅ Valid: Message is authentic
   • ❌ Invalid: Message was altered
   • ➖ None: No DKIM signature

🔑 Key Facts:

• The signature covers both headers and body
• Each domain has its own DKIM keys
• Look for "dkim=pass" in authentication results

💡 Example: A bank email with valid DKIM means:

• It really came from the bank
• No one changed the content

⚠️ Note: DKIM alone doesn't prevent spoofing - always check SPF and DMARC too.

Policy Enforcement (DMARC)

🛡️ What DMARC Does:

• Combines SPF and DKIM checks
• Tells email providers how to handle failures
• Provides reporting about authentication attempts

🚦 Policy Options:

1. None (👀 Monitor): Just track failures
2. Quarantine (🚧): Deliver to spam/junk
3. Reject (🚫): Block completely

📊 Why It Matters:

• Preents domain spoofing
• Gives domain owners control
• Provides visibility into abuse attempts

💡 Example Policy: v=DMARC1; p=quarantine; pct=100; rua=mailto:reports@example.com

• Quarantines failed emails
• Sends reports to example.com

🔒 Best Practice: Start with p=none to monitor, then tighten to quarantine or reject once confident.

Forwarding Protection (ARC)

🔗 What ARC Does:

• Preserves authentication when emails are forwarded
• Creates a verifiable forwarding history
• Helps prevent "broken" authentication from legitimate forwards

🛡️ How It Works:

1. Each forwarding server adds an ARC seal
2. The seal contains authentication results
3. Final recipient can verify the entire chain

🔍 Why It's Important:

• Many legitimate emails get forwarded
• Without ARC, forwards often fail SPF/DKIM
• ARC maintains security through the forwarding chain

💡 Example: A newsletter forwarded from your work email to personal inbox would keep its authentication thanks to ARC.

⚠️ Note: Not all email services support ARC yet. Look for "arc=pass" in authentication results.

Why These Systems Matter

Together, SPF, DKIM, DMARC and ARC create multiple layers of protection against phishing and spoofed emails by verifying messages are really from who they claim to be.