Email delivers more malicious payloads to organisations than any other channel. Phishing links, weaponised attachments, business email compromise, and invoice fraud all arrive through inboxes that employees check dozens of times daily. Basic spam filters catch bulk junk mail effectively, but sophisticated attacks that target specific organisations pass through standard filtering with alarming regularity.
Email authentication protocols form the foundation of a robust email security posture. Sender Policy Framework specifies which mail servers are authorised to send email for your domain. DomainKeys Identified Mail adds cryptographic signatures that verify message integrity. Domain-based Message Authentication, Reporting and Conformance ties these together with policies that tell receiving servers how to handle authentication failures. Together, these protocols dramatically reduce domain spoofing attacks.
Configuring DMARC at enforcement level requires careful planning. Moving too quickly to a reject policy without proper monitoring can block legitimate email from third-party services that send on your behalf. Start with a monitoring policy, analyse the reports to identify all legitimate sending sources, authenticate each one, and then gradually increase enforcement. This phased approach prevents business disruption while building toward full protection.
Advanced threat protection examines email content at a deeper level than traditional filters. Sandboxing detonates attachments in isolated environments to observe malicious behaviour. URL rewriting and time-of-click analysis check links at the moment a user clicks rather than only at delivery time. Machine learning models identify anomalous sending patterns that rules-based filters cannot catch.
Internal email security often receives less attention than inbound filtering. Once an attacker compromises a single email account, they send phishing messages to colleagues from a trusted internal address. These messages bypass external filtering entirely because they originate from within the organisation. Monitoring internal email for suspicious patterns catches account compromise early.
Expert Commentary
William Fieldhouse | Director of Aardwolf Security Ltd
“Email remains the primary attack vector for most organisations, yet many rely on basic spam filtering as their only defence. Properly configured SPF, DKIM, and DMARC records, combined with advanced threat protection and user training, transform email from your biggest weakness into a well-defended channel.”
Regular external network penetration testing that includes email security assessment examines your mail infrastructure from the outside. Testers verify authentication protocol configurations, test filtering effectiveness against current attack techniques, and identify any exposed mail services that attackers could target for credential harvesting or relay abuse.
Attachment policies should restrict file types based on business need rather than allowing everything by default. Executables, scripts, and archive formats that rarely serve legitimate business purposes in email should be blocked or quarantined. For file types that must be allowed, content inspection and sandboxing provide additional protection layers.
Email encryption protects sensitive communications from interception. Opportunistic TLS encryption secures email in transit between mail servers that support it. For highly sensitive communications, end-to-end encryption ensures that only the intended recipient can read the message content. Understanding which communications require which level of protection guides practical encryption policy.
Ongoing vulnerability scanning services monitor your mail infrastructure for configuration drift, expired certificates, and newly discovered vulnerabilities in mail server software. Email servers exposed to the internet require the same rigorous maintenance as any other public-facing service, yet they sometimes escape regular security attention because they are classified as infrastructure rather than applications.
Email security is never finished. Attack techniques evolve constantly, and defences must keep pace. Organisations that layer authentication protocols, advanced filtering, user training, and regular testing build email defences that resist current threats while adapting to whatever comes next.
