What Are Email Security Gateways and Why Should You Care?

Email Security Gateways: The Corporate Digital Bouncers

The Reason Behind A Billion Dollar Industry

You wrote a brilliant email. Personalised it. Tracked it. Hit send. But your client never saw it. Why? Because it got eaten alive by an Email Security Gateway before it even had a chance.

Most people think spam filters live inside Gmail or Outlook. But for many businesses, there’s a whole extra security wall standing between your message and their inbox. These are called Email Security Gateways, and if you are sending to corporate addresses, you need to know what they are and how they think.

So, What Is an Email Security Gateway?

An Email Security Gateway is a separate system that scans, filters and blocks email before it even reaches the recipient’s inbox. It’s the digital equivalent of a nightclub bouncer with a clipboard, an attitude, and a zero-tolerance policy for links that smell suspicious.

They sit in front of the main inbox provider (like Microsoft 365 or Google Workspace) and handle things like:

  • Spam filtering
  • Virus and malware scans
  • Link rewriting and tracking detection
  • Attachment checks
  • Policy enforcement (like blocking marketing emails altogether)

Common names include:

  • Mimecast
  • Barracuda
  • Proofpoint
  • Cisco Email Security
  • Fortinet FortiMail
  • Sophos Email
  • Trend Micro HES
  • SpamTitan
  • IRONSCALES
  • Avanan
  • Libraesva
  • Zix

If your emails are going to corporate inboxes, they are very likely passing through one of these first.

Why Microsoft and Google Just Aren’t Enough

Yes, Microsoft 365 and Google Workspace both have built-in filters. But for many IT departments, they are too basic. They let too much through or don’t give enough control.

Email Security Gateways give IT admins extra tools to:

  • Create custom filtering rules
  • Quarantine suspicious messages
  • Block by domain, language or content type
  • Rewrite links to scan them
  • Strip tracking pixels
  • Prevent spoofing

This means even if your email is technically perfect, it can still be binned by an overprotective filter before the user sees it.

Why This Matters to Marketers and Recruiters

If you are sending to corporate inboxes — and most recruiters are — then you are dealing with these gateways whether you know it or not. That’s why things like SPF, DKIM and DMARC are just table stakes. You need to go further.

Security gateways look for signs of sketchy behaviour:

  • Do your links point to tracking domains?
  • Are you using a URL shortener?
  • Is your subject line aggressive?
  • Do you send too many messages too quickly?
  • Are your headers set up properly?

Even your open tracking pixel can trigger a red flag. Some gateways scan HTML for signs of tracking, remove it, or use sandbox environments to open your email safely. This can mess with your metrics and break your automation logic.

What to Do About It

You cannot bypass these filters. But you can work with them. Here’s how:

  1. Authenticate properly
    SPF, DKIM and DMARC must be correct and aligned. No exceptions.
  2. Use branded tracking domains
    Avoid generic tracking links like trk.mailplatform.com. Use a subdomain of your own site.
  3. Don’t go too heavy on images
    Some gateways flag image-heavy emails as spammy, especially if there’s little text.
  4. Avoid weird link structures
    Bitly, Rebrandly and other URL shorteners are a bad idea. Gateways rewrite them anyway, or worse, block them.
  5. Warm up your domain
    Show these filters that people want your emails. A good warm-up process helps build that trust.
  6. Be ready for rewrites
    Some platforms will rewrite your links and strip your tracking. Plan for that and rely on broader trends, not exact open rates.
  7. Build relationships, not just lists
    A trusted sender address with regular, wanted communication will get through more often than a cold blast from a new domain.

One Last Thing: Admins Are Humans Too

Some IT admins are a bit overzealous. They block marketing emails by default or set filters too tight. This means even the cleanest campaigns can get caught. If you know a contact isn’t receiving your emails, it might be worth asking their IT team to whitelist your domain. Politely.

TL;DR

Email Security Gateways are the hidden layer between you and your recipient. They are powerful, aggressive and absolutely unforgiving of sloppy sending practices. But once you understand how they work, you can shape your strategy to survive their filters and get your message delivered.

Don’t blame Microsoft or Gmail. The real gatekeepers might be sitting quietly in the middle, watching everything.

Need Help Getting Past the Gatekeepers?

At Quinset, we help recruiters and marketers navigate the world of deliverability — including the hidden roadblocks like security gateways. From domain setup to tracking strategies, we help your emails get seen and clicked, not quarantined.

Let’s talk. We speak fluent Barracuda.