How Today’s Attacks Slip Past Your Email Filters and What You Can Do About It

You’ve invested in secure email gateways. You’ve configured Microsoft Defender. Maybe you’ve even layered on spam filters or anti-malware scanning. But phishing emails are still getting through, and your team is still clicking.

This isn’t a failure of your tools. It’s the result of increasingly advanced social engineering tactics and purpose-built messages designed to evade traditional email filters. And unless your cybersecurity strategy evolves beyond the perimeter, you’re leaving your organization open to serious risk.

Let’s break down how attackers are sneaking in and five steps you can take to stop them.

Why Email Filters Aren’t Enough Anymore

Email filters do a good job of catching mass spam and known malware. But today’s phishing campaigns don’t rely on obvious red flags. They use clean infrastructure, zero payloads, and highly personalized content. In other words, they look safe.

Some of the most common tactics attackers now use to bypass your email filters include:

• Zero-link emails: Phishing messages with no links or attachments—just a prompt to reply.
• Domain lookalikes: Impersonated sender addresses that appear nearly identical to real ones.
• HTML obfuscation: Encoded links or hidden scripts that evade detection by scanners.
• Mobile-aware payloads: Content that activates malicious behavior only when opened on a mobile device.
• Timed or geofenced attacks: Emails that behave differently based on time zones or user locations.­­

Each of these tactics is built to blend in and get past traditional filters unnoticed.

Five Smart Defenses You Can Put in Place

1. Understand What’s Slipping Through
   Before you improve your defenses, get visibility. Simulated phishing tests or threat reports from advanced detection tools can help you understand which types of attacks are making it to inboxes and who’s most at risk.
2. Augment Filters with Behavioral Analysis
   Filters scan for patterns and known threats. Behavioral analysis tools go further by evaluating intent, tone, and context. These solutions use AI to flag unusual or manipulative language and can detect impersonation attempts that your filters miss.
3. Empower Users in Real-Time
   Layer in contextual warnings inside emails, like banners alerting users when a message comes from an external or uncommon source. Giving employees that moment of pause can prevent them from taking the bait.
4. Address the Mobile Gap
   Traditional filters often scan for threats based on desktop behavior. However, many phishing tactics now rely on users opening emails on mobile devices, where previews are limited. Simulated smishing and quishing (QR code phishing) campaigns can help users recognize these evolving threats.
5. Prioritize High-Risk Roles
   Certain departments—like HR, finance, and IT—are more likely to be targeted. Tailor training and simulations to match the real threats they face, using personalized attack scenarios and more frequent testing.

Defense in Layers, Not Just Filters

Phishing attacks today aren’t blunt-force threats—they’re subtle, targeted, and engineered to exploit trust. That’s why smart security strategies rely on defense in depth.

Start by evaluating what your filters are missing. Then build in intelligent detection, mobile-aware training, and user reinforcement. Technology alone won’t stop every attack—but a layered approach that includes your people, processes, and tools will dramatically reduce your risk. Yeo & Yeo Technology can help. Contact us.

Information used in this article was provided by our partners at KnowBe4.