Five security risks in your email setup you can't afford to ignore

In the email industry, you may have heard the saying ‘email remains one of the most targeted attack vectors’. This remains true today, with phishing campaigns, business email compromise (BEC), and domain abuse continuing to evolve in both scale and sophistication. In 2025, BEC accounted for more than 3 billion in reported losses according to the FBI's Internet Crime Complaint Center (IC3). At the same time, mailbox providers continue to raise the bar for sender authentication, encryption, and trust, making standards such as DMARC, ARC, and MTA-STS increasingly important. Yet, many businesses continue to rely on platforms deployed 10 years ago with almost the same feature set as to when it was new. They still send and receive messages. It still works… for now.

But underneath the surface, legacy infrastructure introduces a host of significant security risks that become harder to remediate, increasingly expensive to mitigate, and often impossible to eliminate without modernization.

Here are five security risks that could be lurking in your legacy email system.

1. You're running on infrastructure that can’t be properly patched

Organizations running mission-critical infrastructure on operating systems that are no longer actively maintained are not just facing a technical debt problem; they’re facing a security problem.

In 2024, more than 33,000 Common Vulnerabilities and Exposures (CVEs) were published. In 2026, that number is on track to exceed 50,000+ CVEs with over 15,100 CVEs already published in Q1 alone. With new AI-powered tools, the number of reported vulnerabilities is expected to grow even more rapidly in the years ahead.

The growing number of vulnerabilities is only part of the challenge. It’s whether your email infrastructure can be updated quickly when vulnerabilities that affect your environment are discovered. If you’re depending on email infrastructure that no longer receives updates, you’re left with two options: accept the risk or start building workarounds.

Neither option is a long-term strategy designed to help your business flourish. In fact, you’re at risk of exposing your organization to unpatched vulnerabilities and potential security breaches. While it may still be possible to find support from third parties, it would potentially be a fork, which again carries its own security risks. Lucky for you, there’s a third option - move away from unsupported legacy infrastructure to composable email infrastructure.

2. Everybody is scared to touch the configuration

Every long-running platform eventually accumulates custom logic. Whether it’s Lua scripts, policy rules, routing decisions, or integrations, they all solved real problems at some point in time. The issue is what happens years later.

⚠️ Have the original engineers moved on?
⚠️ Is the documentation incomplete?
⚠️ Are there 1000s of lines of code and no one knows what they do?
⚠️ Or is nobody entirely sure what will break if a particular script is modified, and they don’t have the confidence to make those changes?

From a security perspective, that’s a major risk. Because email infrastructure that nobody understands becomes infrastructure that nobody wants to patch, upgrade, or improve. It’s detrimental if you want new features, want to stay competitive, and want to reduce security risks.

3. Your security defenses are frozen in time

Email authentication standards are continuously evolving. DMARC adoption has accelerated. Standards such as ARC, MTA-STS, TLS Reporting, and DANE continue to raise expectations for modern email infrastructure. Even the core standards themselves are still evolving. RFC 9989 (DMARCbis), published earlier this year, updates and refines DMARC based on years of operational experience, while work is underway on the next generation of DomainKeys Identified Mail (DKIM2).

An example of how quickly expectations can change came in 2024 when Google and Yahoo introduced new sender requirements for bulk email senders. Organizations sending large volumes of email were required to implement stronger authentication controls, including SPF, DKIM, and DMARC, while also making it easier for recipients to unsubscribe and report unwanted messages.

For many senders, these requirements were relatively straightforward to implement. For others, particularly those operating older or heavily customized email infrastructure, meeting the new standards required significant effort and coordination across teams. What started as a deliverability initiative quickly became an infrastructure challenge.

The lesson is simple: today's best practice can become tomorrow's baseline requirement. Email infrastructure needs to be capable of adapting to new standards without requiring major projects every time the industry evolves.

4. Upgrades have become projects instead of routine maintenance

One of the clearest signs that you’re on legacy email infrastructure is when upgrades stop being released regularly. Not because teams don’t want to upgrade, but because every upgrade requires a migration project, an infrastructure rebuild, or an extensive testing cycle.

Over time, businesses get stuck, and the platform falls further behind. Security fixes arrive more slowly, and new capabilities never get adopted. For example, a CentOS 7 deployment reached end-of-life in June 2024. Organizations still relying on it must now either migrate to a later version, purchase extended support, or assume additional risk.

Modern email infrastructure should provide you with a clear upgrade path. Staying current should be operational maintenance, not a migration project.

5. Do you have trust issues?

If you’re reading this, chances are you're sending millions or billions of transactional messages, marketing campaigns, or customer communications every day. A compromise doesn't just create a security nightmare; it can:

🚩   impact deliverability
🚩  damage sender reputation
🚩  disrupt customer communications
🚩  erode trust with mailbox providers
🚩  and so much more.

Failing to comply with the latest standards can lead to more than technical risk. It can impact deliverability, brand protection, and customer loyalty. Which combined impacts your bottom line. The cost of outdated infrastructure isn’t only measured in incidents; sometimes it’s measured in lost trust and revenue.

The real security question

For large-scale senders, email infrastructure is one of the most business-critical systems in your tech stack. Most businesses aren’t knowingly ignoring security risks. Because a platform that appears stable can still be running outdated software (hello, CentOS 7), missing critical security updates, and relying on in-house knowledge that no longer exists. The security question is not whether your email infrastructure is functioning today.