Email Security Best Practices
Protect your organisation from the most common—and costly—email threats
From configuration to user behaviour, every layer matters. Explore practical guidance, common pitfalls, and actionable steps drawn from years of experience supporting Mimecast customers and broader secure email operations.
Introduction: Why Email Security Still Fails
Despite the layers of tools available, email remains the most exploited attack vector. Misconfigured policies, outdated DNS records, weak authentication, and unaware users all contribute to incidents—from phishing and spoofing to data loss and ransomware.
Recent examples:
- NHS UK faced spoofing attacks due to lax DMARC enforcement (2024).
- Royal Mail fell victim to a ransomware attack, with the initial compromise believed to have come via email (2023).
What this guide offers:
A curated, field-tested set of best practices to help IT and security leaders reduce risk, improve resilience, and ensure their email ecosystem is configured with intention.
Email Security Best Practices
1. Enforce Strong Authentication with SPF, DKIM, and DMARC
What to do:
- Publish and maintain valid SPF, DKIM, and DMARC records for all sending domains.
- Move to DMARC enforcement (p=reject or quarantine) after monitoring.
- Avoid SPF permerrors and excessive DNS lookups.
🔧 Need help implementing or reviewing? Book a DNS Security Review →
2. Encrypt and Authenticate In-Transit Email with MTA-STS & TLS-RPT
What to do:
- Publish a valid MTA-STS policy in Enforce mode.
- Monitor delivery issues with TLS-RPT.
- Ensure certificates and DNS records are always valid.
🧪 Check your domain with our MTA-STS Readiness Tool →
3. Use AI-Powered Detection to Catch Sophisticated Phishing and BEC
What to do:
- Deploy solutions that analyse behaviour, tone, sender history, and metadata to identify Business Email Compromise and evasive phishing.
- Don't rely solely on static rules or keyword matching.
- Integrate AI engines that learn from your mail flow and adapt to attacker techniques.
💡 Cydaura can help you assess what tools to trust—independent of vendor incentives.
4. Rewrite and Inspect URLs at Click Time
What to do:
- Enable URL rewriting for all inbound mail.
- Apply real-time click protection to inspect the target destination at time-of-click—not just time-of-receipt.
- Enforce policies that block known-bad domains, suspicious redirects, and newly registered domains.
🛡️ Your policies should protect beyond the inbox—especially against delayed payload delivery.
5. Use Sandboxing and AV Together for Attachment Security
What to do:
- Scan all attachments with multi-engine antivirus as a first layer.
- Detonate suspicious files in a sandbox environment to observe behavioural indicators.
- Quarantine or hold files pending analysis where risk thresholds are met.
📎 This is essential to stop zero-days and fileless malware that bypass static detection.
6. Regularly Audit & Optimise Gateway Configuration
What to do:
- Review impersonation protection settings, blocked file types, and threat policies.
- Check for configuration drift from best practices or vendor defaults.
- Validate mail flow logic and rule stacking—especially after service changes or mergers.
📊 Book a Mimecast or M365 Secure Email Review →
7. Apply the Principle of Least Privilege
What to do:
- Limit admin access and use role-based controls for policy management and reporting.
- Enforce MFA on all privileged accounts.
- Review and expire delegated permissions regularly.
🔐 Too much access = too much risk.
8. Run Managed Security Awareness Programs
What to do:
- Deliver tailored, contextual training—not one-size-fits-all videos.
- Use phishing simulations informed by real-world campaigns.
- Track improvement across teams over time.
🧠 Learn how Cydaura's Managed Awareness Training works →
9. Monitor, Report and Improve Continuously
What to do:
- Monitor TLS-RPT, DMARC aggregate and forensic reports, delivery failure logs, and authentication failures.
- Integrate your email security solution's logging with your SOC tools like SIEM & SOAR.
- Monitor Authentication Attempts & Successful Logins to detect compromised accounts.
- Use dashboards to track risk posture over time.
- Schedule quarterly configuration reviews as part of your security operations rhythm.
Why Security Leaders Work with Cydaura
We're a team of former Mimecast experts who've implemented, optimised, and decommissioned secure email platforms for organisations of all sizes. We're 100% independent—so our advice is grounded in your objectives, not software sales.
Whether you're planning to improve your threat detection, achieve regulatory alignment, or phase out an older platform—we help you do it right the first time.