10 Best Anti-Spam & Email Security Software

A Secure Email Gateway (SEG) routes all inbound and outbound email through its external mail servers by changing public DNS MX records. In contrast, an ICES solution connects directly into Microsoft 365 or Google Workspace via cloud Graph APIs. ICES solutions require zero DNS changes, deploy in minutes, and can inspect internal lateral (east-west) emails sent between compromised internal employees.

Business Email Compromise (BEC) involves social engineering where cybercriminals impersonate executives, vendors, or legal counsel to request urgent wire transfers or sensitive payroll data. Because these emails rarely contain traditional malware attachments or known malicious links, legacy signature filters fail to detect them. Modern email security requires conversational AI to analyze tone, relationship history, and display name spoofing.

SPF (Sender Policy Framework) lists the authorized IP addresses allowed to send mail on behalf of a domain. DKIM (DomainKeys Identified Mail) cryptographically signs messages to verify they were not altered in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) dictates how recipient servers should handle emails that fail SPF or DKIM (none, quarantine, or reject) and sends reporting back to domain owners.

Without email continuity protection, incoming emails sent during an M365 outage may bounce back to the sender as undeliverable. Solutions equipped with email continuity spool incoming messages safely in an external cloud queue and provide employees with an emergency webmail portal to continue reading, composing, and replying to messages.

Attackers routinely send emails containing harmless links that lead to legitimate websites, waiting until after the message passes through gateway security filters before weaponizing the destination URL with credential harvesting forms. Time-of-click protection rewrites links and re-analyzes the destination webpage at the exact moment an end-user clicks, blocking access if malicious behavior is detected.

Traditional gateways only inspect north-south traffic (emails entering or exiting the organization). When an attacker steals an internal employee credential via credential stuffing, they use the trusted corporate mailbox to email colleagues, HR, or finance. API-native security continuously scans internal messages to detect compromised accounts immediately.

False positives typically occur when legitimate marketing platforms (e.g., Mailchimp, HubSpot) fail SPF/DKIM alignment, or when newsletters use aggressive tracking redirects. Administrators can prevent false positives by enforcing strict DMARC alignment, establishing IP allowlists for verified transactional services, and tuning spam sensitivity thresholds.

While Microsoft Defender provides a baseline level of filtering, many enterprises supplement or replace it with specialized third-party email security to gain superior BEC conversational AI, faster zero-day attachment sandboxing, dedicated 100% email uptime continuity spooling, and reduced false positives.