SMTP smuggling may not be center stage, but it’s something you need to be on the lookout for.

This tactic poses a severe threat to inboxes by evading traditional email security measures like SPF, DKIM, and DMARC.

SMTP (Simple Mail Transfer Protocol) is the backbone of email communication, dictating how emails are transmitted between servers. But, like with every digital interface and protocol, there’s potential for manipulation, allowing cybercriminals to exploit a series of miscommunications enabling successful transmission of impersonated emails to unsuspecting recipients.

At its core, SMTP smuggling hinges on crafty manipulation of the end-of-data sequence during email transmission. By embedding entire emails within this process, threat actors bypass checkpoints, which include verification of SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance). The point is to jam the bad behind the good within the legitimate email flow, leading to a potential breach and heightened vulnerability.

Impersonation attacks are forecasted to increase in 2024 and SMTP smuggling can facilitate impersonation attacks. Those unaware of what SMTP smuggling looks like are susceptible to falling prey to this social engineering scam. Deceiving unsuspecting users has always been the goal for cybercriminals and it’s unlikely to change as they continue to leverage new means and tools to expand their attacks.

Some providers, like Microsoft, have swiftly deployed patches to address this potential threat while others could still be allowing systems to be exposed to potential exploitation.

In the wake of continually emerging threats, organizations must prioritize comprehensive security awareness training for their workforce. Platforms like KnowBe4 stand as beacons, empowering over 65,000 organizations globally to fortify their security culture and mitigate human-related risks.

Collaborative efforts between security researchers, industry players and organizations, and end users remain crucial to staying ahead of sophisticated threats like SMTP smuggling. Heightened awareness, swift vendor response, and proactive security measures can collectively keep us safer in the battle against evolving cybercrime efforts.