Email Security Best Practices 2024: Complete Guide

Email remains the primary attack vector for cybercriminals. In 2024, with stricter requirements from major providers and evolving threats, implementing comprehensive email security has never been more important.

The 2024 Email Security Landscape

Key Changes in 2024

Google & Yahoo Requirements (February 2024):

• SPF or DKIM required for all senders
• DMARC required for bulk senders
• One-click unsubscribe mandatory
• Spam rate must be below 0.3%

Microsoft Requirements (2025):

• Similar authentication requirements
• DMARC enforcement for Outlook.com

Threat Evolution:

• AI-powered phishing attacks
• Business Email Compromise (BEC) increasing
• Supply chain email attacks
• Deepfake voice/video paired with email

Authentication: The Foundation

The Authentication Stack

Every organization needs all three:

SPF Best Practices

Do:

• ✅ Include all legitimate sending sources
• ✅ End with -all (hard fail)
• ✅ Stay under 10 DNS lookups
• ✅ Audit quarterly

Don't:

• ❌ Use +all (allows anyone)
• ❌ Have multiple SPF records
• ❌ Forget third-party services
• ❌ Neglect maintenance

Example:

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

DKIM Best Practices

Do:

• ✅ Use 2048-bit keys
• ✅ Enable for all sending services
• ✅ Rotate keys annually
• ✅ Sign important headers (From, To, Subject)

Don't:

• ❌ Use 512 or 768-bit keys
• ❌ Share private keys
• ❌ Forget new services
• ❌ Ignore DKIM failures

DMARC Best Practices

Do:

• ✅ Start with p=none for monitoring
• ✅ Use aggregate reports (rua=)
• ✅ Progress to p=reject
• ✅ Monitor continuously

Don't:

• ❌ Jump straight to p=reject
• ❌ Ignore DMARC reports
• ❌ Forget subdomain policies
• ❌ "Set and forget"

Progression:

1. Week 1-4: p=none (monitor)
2. Week 5-8: p=quarantine; pct=10
3. Week 9-12: p=quarantine; pct=50
4. Week 13+: p=reject

Advanced Security Measures

MTA-STS

What it does: Enforces TLS encryption for email delivery.

Why it matters: Prevents man-in-the-middle attacks and email interception.

Implementation:

# DNS: _mta-sts.example.com TXT
v=STSv1; id=20240101
 
# Policy file: https://mta-sts.example.com/.well-known/mta-sts.txt
version: STSv1
mode: enforce
mx: mail.example.com
max_age: 604800

TLS-RPT

What it does: Provides reports on TLS delivery failures.

Implementation:

# DNS: _smtp._tls.example.com TXT
v=TLSRPTv1; rua=mailto:tls-reports@example.com

BIMI

What it does: Displays your brand logo in email clients.

Requirements:

• DMARC at enforcement (p=quarantine or p=reject)
• SVG logo in BIMI format
• VMC certificate (for Gmail/Apple)

Benefits:

• Brand visibility
• Trust signals
• Higher engagement

DANE

What it does: Associates TLS certificates with DNS.

Use case: High-security environments requiring certificate pinning.

Phishing Prevention

Technical Controls

1. Email Authentication (SPF, DKIM, DMARC)

• Prevents domain spoofing
• Blocks unauthorized senders
• Provides visibility

2. Email Filtering

• Spam detection
• Malware scanning
• Link analysis
• Attachment sandboxing

3. URL Rewriting

• Click-time URL analysis
• Redirect protection
• Safe links

4. Impersonation Protection

• Display name analysis
• Look-alike domain detection
• VIP protection

Human Controls

1. Security Awareness Training

• Regular phishing simulations
• Reporting mechanisms
• Ongoing education

2. Verification Procedures

• Wire transfer verification
• Sensitive request callbacks
• Out-of-band confirmation

3. Reporting Culture

• Easy reporting process
• No blame for mistakes
• Positive reinforcement

Compliance Requirements

Regulatory Frameworks

DMARC for Compliance

DMARC helps meet requirements by:

• Demonstrating security controls
• Providing audit trails (reports)
• Preventing unauthorized email
• Protecting customer data

Documentation Requirements

Maintain records of:

• Authentication configurations
• Policy decisions
• Monitoring procedures
• Incident responses
• Training completion

Operational Security

Monitoring

Daily:

• Authentication pass rates
• Spam complaint rates
• Blacklist status
• Anomaly alerts

Weekly:

• DMARC report review
• Source analysis
• Trend identification
• Issue remediation

Monthly:

• Comprehensive audit
• Compliance review
• Training updates
• Policy adjustments

Incident Response

Email Security Incident Playbook:

1. Detection

   • Alert received
   • Issue identified
   • Scope assessed

2. Containment

   • Block malicious sources
   • Update authentication
   • Notify affected parties

3. Investigation

   • Analyze DMARC reports
   • Review logs
   • Identify root cause

4. Remediation

   • Fix configuration
   • Update policies
   • Implement controls

5. Recovery

   • Verify fix
   • Monitor closely
   • Document lessons

Employee Guidelines

Email Security Policies

Users should:

• ✅ Verify unexpected requests
• ✅ Report suspicious emails
• ✅ Use strong passwords
• ✅ Enable MFA
• ✅ Be cautious with attachments
• ✅ Verify links before clicking

Users should not:

• ❌ Click links in suspicious emails
• ❌ Open unexpected attachments
• ❌ Send sensitive data via email
• ❌ Ignore security warnings
• ❌ Forward suspicious emails (report instead)

Executive Protection

Executives face targeted attacks:

• Whaling: Phishing targeting executives
• BEC: Business email compromise
• Impersonation: Attackers pretending to be executives

Protections:

• Enhanced monitoring
• Out-of-band verification
• Dedicated security training
• VIP mailbox protection

Security Tools Checklist

Essential Tools

• DMARC Monitoring (MailSentinel)
• Email Gateway (spam/malware filtering)
• Security Awareness Platform (training)
• Incident Response Tools (logging, analysis)

Nice to Have

• Email Encryption (S/MIME, PGP)
• Data Loss Prevention (DLP)
• Advanced Threat Protection (sandboxing)
• SIEM Integration (security monitoring)

2024 Action Plan

Immediate (This Week)

1. Audit current SPF, DKIM, DMARC
2. Set up DMARC monitoring
3. Review authentication pass rates
4. Identify configuration gaps

Short-Term (This Month)

1. Fix authentication issues
2. Update SPF for all services
3. Enable DKIM everywhere
4. Progress DMARC toward enforcement

Medium-Term (This Quarter)

1. Achieve DMARC enforcement
2. Implement MTA-STS
3. Set up TLS-RPT
4. Consider BIMI

Long-Term (This Year)

1. Continuous monitoring
2. Regular audits
3. Training program
4. Incident response exercises

Resources

• DMARC Setup Guide - Complete configuration
• Email Authentication Checklist - Step-by-step
• BIMI Guide - Brand logos in email
• MTA-STS Guide - TLS enforcement
• DMARC FAQ - Common questions

Start Securing Your Email →