Email Security Best Practices

Comprehensive guide to protecting your domain and users from email-based threats, phishing attacks, and brand impersonation.

Why Email Security Matters

Email remains the primary attack vector for cybercriminals. Without proper authentication, attackers can send emails that appear to come from your domain, damaging your reputation and targeting your customers with phishing attacks.

1. Implement All Three Authentication Protocols

SPF (Sender Policy Framework)

SPF specifies which mail servers are authorized to send email on behalf of your domain. This prevents attackers from forging your domain in the email's envelope sender.

Example SPF Record:

v=spf1 include:_spf.google.com include:sendgrid.net -all

Best Practices:

  • Use -all (hard fail) instead of ~all (soft fail) for maximum protection
  • Keep DNS lookups under 10 to avoid validation failures
  • Use ip4: and ip6: mechanisms instead of include: when possible
  • Regularly audit and remove outdated entries

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to your emails, allowing receivers to verify that messages haven't been tampered with in transit and actually came from your domain.

Best Practices:

  • Use 2048-bit RSA keys minimum (recommended over 1024-bit)
  • Rotate DKIM keys annually for security
  • Use multiple selectors for different mail streams
  • Keep private keys secure and never expose them
  • Test DKIM signing before full deployment

DMARC (Domain-based Message Authentication)

DMARC builds on SPF and DKIM by telling receiving mail servers what to do when authentication fails. It also provides reporting so you can monitor email activity.

DMARC Deployment Strategy:

1

Start with monitoring (p=none)

Deploy for 2-4 weeks to understand your email ecosystem

2

Review reports

Identify all legitimate email sources and ensure they pass SPF or DKIM

3

Move to quarantine (p=quarantine)

Failed emails go to spam folders

4

Finally, reject (p=reject)

Failed emails are blocked entirely for maximum protection

2. Additional Security Measures

Enable TLS for Email Transport

Transport Layer Security (TLS) encrypts email in transit between mail servers, preventing eavesdropping and man-in-the-middle attacks.

  • MTA-STS: Forces encrypted connections for email delivery
  • DANE: Uses DNSSEC to verify TLS certificates
  • TLS Reporting: Get reports on TLS failures and connection issues

BIMI (Brand Indicators for Message Identification)

BIMI displays your brand logo next to authenticated emails in supported email clients, helping users recognize legitimate emails from your organization.

Note: BIMI requires DMARC enforcement (p=quarantine or p=reject) and a Verified Mark Certificate (VMC) for most email providers.

Subdomain Protection

Don't forget to protect your subdomains! Attackers often target unprotected subdomains to send spoofed emails.

Protect All Subdomains:

  • Use sp=reject in your DMARC policy to apply to all subdomains
  • Create explicit DMARC records for subdomains that send email
  • Use wildcard DNS records for unused subdomains: *._domainkey TXT "v=DKIM1; p="

3. Continuous Monitoring and Maintenance

Monitor DMARC Reports

DMARC reports provide valuable insights into your email authentication status and potential threats targeting your domain.

Aggregate Reports (RUA)

Daily summaries of authentication results

Forensic Reports (RUF)

Individual failure samples for investigation

Monthly Security Checklist

  • Review DMARC reports for suspicious activity
  • Verify all authentication records are still valid
  • Check for DNS propagation issues
  • Update SPF record when adding/removing email services
  • Test email deliverability to major providers
  • Review and update security documentation

4. User Education and Awareness

Technical controls are only part of the solution. Educating your users about email security is crucial for preventing successful phishing attacks.

Recognize Phishing

  • •Verify sender addresses carefully
  • •Look for spelling and grammar errors
  • •Hover over links before clicking
  • •Be suspicious of urgent requests

Security Programs

  • •Regular phishing simulations
  • •Quarterly security training
  • •Clear reporting procedures
  • •Recognition for threat reporting

Check Your Email Security Now

See how your domain stacks up against these best practices.

Check Your DomainSetup Guide

Related Resources

Complete DMARC Setup GuideDMARC vs SPF vs DKIMTroubleshooting Common IssuesFree DMARC Checker

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